fix: small issues

Updated mock AAC transcoding command to use the new default (ipod with
fragmented MP4) matching the migration, ensuring tests exercise the same
buildDynamicArgs code path as production. Improved archiver test mock to
match on the whole StreamRequest struct instead of decomposing fields,
making it resilient to future field additions. Added named constants for
JWT claim keys in the transcode token and wrapped ParseTranscodeParams
errors with ErrTokenInvalid for consistency. Documented the IsLossless
BitDepth fallback heuristic as temporary until Codec column is populated.

Signed-off-by: Deluan <deluan@navidrome.org>

adapters/gotaglib/gotaglib.go

@@ -65,6 +65,7 @@ func (e extractor) extractMetadata(filePath string) (*metadata.Info, error) {
 		Channels:   int(props.Channels),
 		SampleRate: int(props.SampleRate),
 		BitDepth:   int(props.BitsPerSample),
+		Codec:      props.Codec,
 	}
 
 	// Convert normalized tags to lowercase keys (go-taglib returns UPPERCASE keys)

cmd/wire_gen.go

@@ -19,6 +19,7 @@ import (
 	"github.com/navidrome/navidrome/core/metrics"
 	"github.com/navidrome/navidrome/core/playback"
 	"github.com/navidrome/navidrome/core/scrobbler"
+	"github.com/navidrome/navidrome/core/transcode"
 	"github.com/navidrome/navidrome/db"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/persistence"
@@ -102,7 +103,8 @@ func CreateSubsonicAPIRouter(ctx context.Context) *subsonic.Router {
 	modelScanner := scanner.New(ctx, dataStore, cacheWarmer, broker, playlists, metricsMetrics)
 	playTracker := scrobbler.GetPlayTracker(dataStore, broker, manager)
 	playbackServer := playback.GetInstance(dataStore)
-	router := subsonic.New(dataStore, artworkArtwork, mediaStreamer, archiver, players, provider, modelScanner, broker, playlists, playTracker, share, playbackServer, metricsMetrics)
+	decider := transcode.NewDecider(dataStore)
+	router := subsonic.New(dataStore, artworkArtwork, mediaStreamer, archiver, players, provider, modelScanner, broker, playlists, playTracker, share, playbackServer, metricsMetrics, decider)
 	return router
 }
 

consts/consts.go

@@ -151,7 +151,13 @@ var (
 			Name:           "aac audio",
 			TargetFormat:   "aac",
 			DefaultBitRate: 256,
-			Command:        "ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a aac -f adts -",
+			Command:        "ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a aac -f ipod -movflags frag_keyframe+empty_moov -",
+		},
+		{
+			Name:           "flac audio",
+			TargetFormat:   "flac",
+			DefaultBitRate: 0,
+			Command:        "ffmpeg -i %s -ss %t -map 0:a:0 -v 0 -c:a flac -f flac -",
 		},
 	}
 )

core/archiver.go

@@ -176,7 +176,7 @@ func (a *archiver) addFileToZip(ctx context.Context, z *zip.Writer, mf model.Med
 
 	var r io.ReadCloser
 	if format != "raw" && format != "" {
-		r, err = a.ms.DoStream(ctx, &mf, format, bitrate, 0)
+		r, err = a.ms.DoStream(ctx, &mf, StreamRequest{Format: format, BitRate: bitrate})
 	} else {
 		r, err = os.Open(path)
 	}

core/archiver_test.go

@@ -44,7 +44,7 @@ var _ = Describe("Archiver", func() {
 			}}).Return(mfs, nil)
 
 			ds.On("MediaFile", mock.Anything).Return(mfRepo)
-			ms.On("DoStream", mock.Anything, mock.Anything, "mp3", 128, 0).Return(io.NopCloser(strings.NewReader("test")), nil).Times(3)
+			ms.On("DoStream", mock.Anything, mock.Anything, core.StreamRequest{Format: "mp3", BitRate: 128}).Return(io.NopCloser(strings.NewReader("test")), nil).Times(3)
 
 			out := new(bytes.Buffer)
 			err := arch.ZipAlbum(context.Background(), "1", "mp3", 128, out)
@@ -73,7 +73,7 @@ var _ = Describe("Archiver", func() {
 			}}).Return(mfs, nil)
 
 			ds.On("MediaFile", mock.Anything).Return(mfRepo)
-			ms.On("DoStream", mock.Anything, mock.Anything, "mp3", 128, 0).Return(io.NopCloser(strings.NewReader("test")), nil).Times(2)
+			ms.On("DoStream", mock.Anything, mock.Anything, core.StreamRequest{Format: "mp3", BitRate: 128}).Return(io.NopCloser(strings.NewReader("test")), nil).Times(2)
 
 			out := new(bytes.Buffer)
 			err := arch.ZipArtist(context.Background(), "1", "mp3", 128, out)
@@ -104,7 +104,7 @@ var _ = Describe("Archiver", func() {
 			}
 
 			sh.On("Load", mock.Anything, "1").Return(share, nil)
-			ms.On("DoStream", mock.Anything, mock.Anything, "mp3", 128, 0).Return(io.NopCloser(strings.NewReader("test")), nil).Times(2)
+			ms.On("DoStream", mock.Anything, mock.Anything, core.StreamRequest{Format: "mp3", BitRate: 128}).Return(io.NopCloser(strings.NewReader("test")), nil).Times(2)
 
 			out := new(bytes.Buffer)
 			err := arch.ZipShare(context.Background(), "1", out)
@@ -136,7 +136,7 @@ var _ = Describe("Archiver", func() {
 			plRepo := &mockPlaylistRepository{}
 			plRepo.On("GetWithTracks", "1", true, false).Return(pls, nil)
 			ds.On("Playlist", mock.Anything).Return(plRepo)
-			ms.On("DoStream", mock.Anything, mock.Anything, "mp3", 128, 0).Return(io.NopCloser(strings.NewReader("test")), nil).Times(2)
+			ms.On("DoStream", mock.Anything, mock.Anything, core.StreamRequest{Format: "mp3", BitRate: 128}).Return(io.NopCloser(strings.NewReader("test")), nil).Times(2)
 
 			out := new(bytes.Buffer)
 			err := arch.ZipPlaylist(context.Background(), "1", "mp3", 128, out)
@@ -217,8 +217,8 @@ type mockMediaStreamer struct {
 	core.MediaStreamer
 }
 
-func (m *mockMediaStreamer) DoStream(ctx context.Context, mf *model.MediaFile, reqFormat string, reqBitRate int, reqOffset int) (*core.Stream, error) {
+func (m *mockMediaStreamer) DoStream(ctx context.Context, mf *model.MediaFile, req core.StreamRequest) (*core.Stream, error) {
-	args := m.Called(ctx, mf, reqFormat, reqBitRate, reqOffset)
+	args := m.Called(ctx, mf, req)
 	if args.Error(1) != nil {
 		return nil, args.Error(1)
 	}

core/ffmpeg/ffmpeg.go

@@ -12,11 +12,24 @@ import (
 	"sync"
 
 	"github.com/navidrome/navidrome/conf"
+	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/log"
 )
 
+// TranscodeOptions contains all parameters for a transcoding operation.
+type TranscodeOptions struct {
+	Command    string // DB command template (used to detect custom vs default)
+	Format     string // Target format (mp3, opus, aac, flac)
+	FilePath   string
+	BitRate    int // kbps, 0 = codec default
+	SampleRate int // 0 = no constraint
+	Channels   int // 0 = no constraint
+	BitDepth   int // 0 = no constraint; valid values: 16, 24, 32
+	Offset     int // seconds
+}
+
 type FFmpeg interface {
-	Transcode(ctx context.Context, command, path string, maxBitRate, offset int) (io.ReadCloser, error)
+	Transcode(ctx context.Context, opts TranscodeOptions) (io.ReadCloser, error)
 	ExtractImage(ctx context.Context, path string) (io.ReadCloser, error)
 	Probe(ctx context.Context, files []string) (string, error)
 	CmdPath() (string, error)
@@ -35,15 +48,19 @@ const (
 
 type ffmpeg struct{}
 
-func (e *ffmpeg) Transcode(ctx context.Context, command, path string, maxBitRate, offset int) (io.ReadCloser, error) {
+func (e *ffmpeg) Transcode(ctx context.Context, opts TranscodeOptions) (io.ReadCloser, error) {
 	if _, err := ffmpegCmd(); err != nil {
 		return nil, err
 	}
-	// First make sure the file exists
+	if err := fileExists(opts.FilePath); err != nil {
-	if err := fileExists(path); err != nil {
 		return nil, err
 	}
-	args := createFFmpegCommand(command, path, maxBitRate, offset)
+	var args []string
+	if isDefaultCommand(opts.Format, opts.Command) {
+		args = buildDynamicArgs(opts)
+	} else {
+		args = buildTemplateArgs(opts)
+	}
 	return e.start(ctx, args)
 }
 
@@ -51,7 +68,6 @@ func (e *ffmpeg) ExtractImage(ctx context.Context, path string) (io.ReadCloser,
 	if _, err := ffmpegCmd(); err != nil {
 		return nil, err
 	}
-	// First make sure the file exists
 	if err := fileExists(path); err != nil {
 		return nil, err
 	}
@@ -156,6 +172,139 @@ func (j *ffCmd) wait() {
 	_ = j.out.Close()
 }
 
+// formatCodecMap maps target format to ffmpeg codec flag.
+var formatCodecMap = map[string]string{
+	"mp3":  "libmp3lame",
+	"opus": "libopus",
+	"aac":  "aac",
+	"flac": "flac",
+}
+
+// formatOutputMap maps target format to ffmpeg output format flag (-f).
+var formatOutputMap = map[string]string{
+	"mp3":  "mp3",
+	"opus": "opus",
+	"aac":  "ipod",
+	"flac": "flac",
+}
+
+// defaultCommands is used to detect whether a user has customized their transcoding command.
+var defaultCommands = func() map[string]string {
+	m := make(map[string]string, len(consts.DefaultTranscodings))
+	for _, t := range consts.DefaultTranscodings {
+		m[t.TargetFormat] = t.Command
+	}
+	return m
+}()
+
+// isDefaultCommand returns true if the command matches the known default for this format.
+func isDefaultCommand(format, command string) bool {
+	return defaultCommands[format] == command
+}
+
+// buildDynamicArgs programmatically constructs ffmpeg arguments for known formats,
+// including all transcoding parameters (bitrate, sample rate, channels).
+func buildDynamicArgs(opts TranscodeOptions) []string {
+	cmdPath, _ := ffmpegCmd()
+	args := []string{cmdPath, "-i", opts.FilePath}
+
+	if opts.Offset > 0 {
+		args = append(args, "-ss", strconv.Itoa(opts.Offset))
+	}
+
+	args = append(args, "-map", "0:a:0")
+
+	if codec, ok := formatCodecMap[opts.Format]; ok {
+		args = append(args, "-c:a", codec)
+	}
+
+	if opts.BitRate > 0 {
+		args = append(args, "-b:a", strconv.Itoa(opts.BitRate)+"k")
+	}
+	if opts.SampleRate > 0 {
+		args = append(args, "-ar", strconv.Itoa(opts.SampleRate))
+	}
+	if opts.Channels > 0 {
+		args = append(args, "-ac", strconv.Itoa(opts.Channels))
+	}
+	// Only pass -sample_fmt for lossless output formats where bit depth matters.
+	// Lossy codecs (mp3, aac, opus) handle sample format conversion internally,
+	// and passing interleaved formats like "s16" causes silent failures.
+	if opts.BitDepth >= 16 && isLosslessOutputFormat(opts.Format) {
+		args = append(args, "-sample_fmt", bitDepthToSampleFmt(opts.BitDepth))
+	}
+
+	args = append(args, "-v", "0")
+
+	if outputFmt, ok := formatOutputMap[opts.Format]; ok {
+		args = append(args, "-f", outputFmt)
+	}
+
+	// For AAC in MP4 container, enable fragmented MP4 for pipe-safe streaming
+	if opts.Format == "aac" {
+		args = append(args, "-movflags", "frag_keyframe+empty_moov")
+	}
+
+	args = append(args, "-")
+	return args
+}
+
+// buildTemplateArgs handles user-customized command templates, with dynamic injection
+// of sample rate and channels when the template doesn't already include them.
+func buildTemplateArgs(opts TranscodeOptions) []string {
+	args := createFFmpegCommand(opts.Command, opts.FilePath, opts.BitRate, opts.Offset)
+
+	// Dynamically inject -ar, -ac, and -sample_fmt for custom templates that don't include them
+	if opts.SampleRate > 0 {
+		args = injectBeforeOutput(args, "-ar", strconv.Itoa(opts.SampleRate))
+	}
+	if opts.Channels > 0 {
+		args = injectBeforeOutput(args, "-ac", strconv.Itoa(opts.Channels))
+	}
+	if opts.BitDepth >= 16 && isLosslessOutputFormat(opts.Format) {
+		args = injectBeforeOutput(args, "-sample_fmt", bitDepthToSampleFmt(opts.BitDepth))
+	}
+	return args
+}
+
+// injectBeforeOutput inserts a flag and value before the trailing "-" (stdout output).
+func injectBeforeOutput(args []string, flag, value string) []string {
+	if len(args) > 0 && args[len(args)-1] == "-" {
+		result := make([]string, 0, len(args)+2)
+		result = append(result, args[:len(args)-1]...)
+		result = append(result, flag, value, "-")
+		return result
+	}
+	return append(args, flag, value)
+}
+
+// isLosslessOutputFormat returns true if the format is a lossless audio format
+// where preserving bit depth via -sample_fmt is meaningful.
+// Note: this covers only formats ffmpeg can produce as output. For the full set of
+// lossless formats used in transcoding decisions, see core/transcode/codec.go:isLosslessFormat.
+func isLosslessOutputFormat(format string) bool {
+	switch strings.ToLower(format) {
+	case "flac", "alac", "wav", "aiff":
+		return true
+	}
+	return false
+}
+
+// bitDepthToSampleFmt converts a bit depth value to the ffmpeg sample_fmt string.
+// FLAC only supports s16 and s32; for 24-bit sources, s32 is the correct format
+// (ffmpeg packs 24-bit samples into 32-bit containers).
+func bitDepthToSampleFmt(bitDepth int) string {
+	switch bitDepth {
+	case 16:
+		return "s16"
+	case 32:
+		return "s32"
+	default:
+		// 24-bit and other depths: use s32 (the next valid container size)
+		return "s32"
+	}
+}
+
 // Path will always be an absolute path
 func createFFmpegCommand(cmd, path string, maxBitRate, offset int) []string {
 	var args []string

core/ffmpeg/ffmpeg_test.go

@@ -2,19 +2,27 @@ package ffmpeg
 
 import (
 	"context"
+	"os"
+	"path/filepath"
 	"runtime"
 	sync "sync"
 	"testing"
 	"time"
 
+	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/log"
-	"github.com/navidrome/navidrome/tests"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
 
 func TestFFmpeg(t *testing.T) {
-	tests.Init(t, false)
+	// Inline test init to avoid import cycle with tests package
+	//nolint:dogsled
+	_, file, _, _ := runtime.Caller(0)
+	appPath, _ := filepath.Abs(filepath.Join(filepath.Dir(file), "..", ".."))
+	confPath := filepath.Join(appPath, "tests", "navidrome-test.toml")
+	_ = os.Chdir(appPath)
+	conf.LoadFromFile(confPath)
 	log.SetLevel(log.LevelFatal)
 	RegisterFailHandler(Fail)
 	RunSpecs(t, "FFmpeg Suite")
@@ -70,6 +78,286 @@ var _ = Describe("ffmpeg", func() {
 		})
 	})
 
+	Describe("isDefaultCommand", func() {
+		It("returns true for known default mp3 command", func() {
+			Expect(isDefaultCommand("mp3", "ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -f mp3 -")).To(BeTrue())
+		})
+		It("returns true for known default opus command", func() {
+			Expect(isDefaultCommand("opus", "ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a libopus -f opus -")).To(BeTrue())
+		})
+		It("returns true for known default aac command", func() {
+			Expect(isDefaultCommand("aac", "ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a aac -f ipod -movflags frag_keyframe+empty_moov -")).To(BeTrue())
+		})
+		It("returns true for known default flac command", func() {
+			Expect(isDefaultCommand("flac", "ffmpeg -i %s -ss %t -map 0:a:0 -v 0 -c:a flac -f flac -")).To(BeTrue())
+		})
+		It("returns false for a custom command", func() {
+			Expect(isDefaultCommand("mp3", "ffmpeg -i %s -b:a %bk -custom-flag -f mp3 -")).To(BeFalse())
+		})
+		It("returns false for unknown format", func() {
+			Expect(isDefaultCommand("wav", "ffmpeg -i %s -f wav -")).To(BeFalse())
+		})
+	})
+
+	Describe("buildDynamicArgs", func() {
+		It("builds mp3 args with bitrate, samplerate, and channels", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:     "mp3",
+				FilePath:   "/music/file.flac",
+				BitRate:    256,
+				SampleRate: 48000,
+				Channels:   2,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-map", "0:a:0",
+				"-c:a", "libmp3lame",
+				"-b:a", "256k",
+				"-ar", "48000",
+				"-ac", "2",
+				"-v", "0",
+				"-f", "mp3",
+				"-",
+			}))
+		})
+
+		It("builds flac args without bitrate", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:     "flac",
+				FilePath:   "/music/file.dsf",
+				SampleRate: 48000,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.dsf",
+				"-map", "0:a:0",
+				"-c:a", "flac",
+				"-ar", "48000",
+				"-v", "0",
+				"-f", "flac",
+				"-",
+			}))
+		})
+
+		It("builds opus args with bitrate only", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "opus",
+				FilePath: "/music/file.flac",
+				BitRate:  128,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-map", "0:a:0",
+				"-c:a", "libopus",
+				"-b:a", "128k",
+				"-v", "0",
+				"-f", "opus",
+				"-",
+			}))
+		})
+
+		It("includes offset when specified", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "mp3",
+				FilePath: "/music/file.mp3",
+				BitRate:  192,
+				Offset:   30,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.mp3",
+				"-ss", "30",
+				"-map", "0:a:0",
+				"-c:a", "libmp3lame",
+				"-b:a", "192k",
+				"-v", "0",
+				"-f", "mp3",
+				"-",
+			}))
+		})
+
+		It("builds aac args with fragmented MP4 container", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "aac",
+				FilePath: "/music/file.flac",
+				BitRate:  256,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-map", "0:a:0",
+				"-c:a", "aac",
+				"-b:a", "256k",
+				"-v", "0",
+				"-f", "ipod",
+				"-movflags", "frag_keyframe+empty_moov",
+				"-",
+			}))
+		})
+
+		It("builds flac args with bit depth", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "flac",
+				FilePath: "/music/file.dsf",
+				BitDepth: 24,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.dsf",
+				"-map", "0:a:0",
+				"-c:a", "flac",
+				"-sample_fmt", "s32",
+				"-v", "0",
+				"-f", "flac",
+				"-",
+			}))
+		})
+
+		It("omits -sample_fmt when bit depth is 0", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "flac",
+				FilePath: "/music/file.flac",
+				BitDepth: 0,
+			})
+			Expect(args).ToNot(ContainElement("-sample_fmt"))
+		})
+
+		It("omits -sample_fmt when bit depth is too low (DSD)", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "flac",
+				FilePath: "/music/file.dsf",
+				BitDepth: 1,
+			})
+			Expect(args).ToNot(ContainElement("-sample_fmt"))
+		})
+
+		It("omits -sample_fmt for mp3 even when bit depth >= 16", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "mp3",
+				FilePath: "/music/file.flac",
+				BitRate:  256,
+				BitDepth: 16,
+			})
+			Expect(args).ToNot(ContainElement("-sample_fmt"))
+		})
+
+		It("omits -sample_fmt for aac even when bit depth >= 16", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "aac",
+				FilePath: "/music/file.flac",
+				BitRate:  256,
+				BitDepth: 16,
+			})
+			Expect(args).ToNot(ContainElement("-sample_fmt"))
+		})
+
+		It("omits -sample_fmt for opus even when bit depth >= 16", func() {
+			args := buildDynamicArgs(TranscodeOptions{
+				Format:   "opus",
+				FilePath: "/music/file.flac",
+				BitRate:  128,
+				BitDepth: 16,
+			})
+			Expect(args).ToNot(ContainElement("-sample_fmt"))
+		})
+	})
+
+	Describe("bitDepthToSampleFmt", func() {
+		It("converts 16-bit", func() {
+			Expect(bitDepthToSampleFmt(16)).To(Equal("s16"))
+		})
+		It("converts 24-bit to s32 (FLAC only supports s16/s32)", func() {
+			Expect(bitDepthToSampleFmt(24)).To(Equal("s32"))
+		})
+		It("converts 32-bit", func() {
+			Expect(bitDepthToSampleFmt(32)).To(Equal("s32"))
+		})
+	})
+
+	Describe("buildTemplateArgs", func() {
+		It("injects -ar and -ac into custom template", func() {
+			args := buildTemplateArgs(TranscodeOptions{
+				Command:    "ffmpeg -i %s -b:a %bk -v 0 -f mp3 -",
+				FilePath:   "/music/file.flac",
+				BitRate:    192,
+				SampleRate: 44100,
+				Channels:   2,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-b:a", "192k", "-v", "0", "-f", "mp3",
+				"-ar", "44100", "-ac", "2",
+				"-",
+			}))
+		})
+
+		It("injects only -ar when channels is 0", func() {
+			args := buildTemplateArgs(TranscodeOptions{
+				Command:    "ffmpeg -i %s -b:a %bk -v 0 -f mp3 -",
+				FilePath:   "/music/file.flac",
+				BitRate:    192,
+				SampleRate: 48000,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-b:a", "192k", "-v", "0", "-f", "mp3",
+				"-ar", "48000",
+				"-",
+			}))
+		})
+
+		It("does not inject anything when sample rate and channels are 0", func() {
+			args := buildTemplateArgs(TranscodeOptions{
+				Command:  "ffmpeg -i %s -b:a %bk -v 0 -f mp3 -",
+				FilePath: "/music/file.flac",
+				BitRate:  192,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-b:a", "192k", "-v", "0", "-f", "mp3",
+				"-",
+			}))
+		})
+
+		It("injects -sample_fmt for lossless output format with bit depth", func() {
+			args := buildTemplateArgs(TranscodeOptions{
+				Command:  "ffmpeg -i %s -v 0 -c:a flac -f flac -",
+				Format:   "flac",
+				FilePath: "/music/file.dsf",
+				BitDepth: 24,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.dsf",
+				"-v", "0", "-c:a", "flac", "-f", "flac",
+				"-sample_fmt", "s32",
+				"-",
+			}))
+		})
+
+		It("does not inject -sample_fmt for lossy output format even with bit depth", func() {
+			args := buildTemplateArgs(TranscodeOptions{
+				Command:  "ffmpeg -i %s -b:a %bk -v 0 -f mp3 -",
+				Format:   "mp3",
+				FilePath: "/music/file.flac",
+				BitRate:  192,
+				BitDepth: 16,
+			})
+			Expect(args).To(Equal([]string{
+				"ffmpeg", "-i", "/music/file.flac",
+				"-b:a", "192k", "-v", "0", "-f", "mp3",
+				"-",
+			}))
+		})
+	})
+
+	Describe("injectBeforeOutput", func() {
+		It("inserts flag before trailing dash", func() {
+			args := injectBeforeOutput([]string{"ffmpeg", "-i", "file.mp3", "-f", "mp3", "-"}, "-ar", "48000")
+			Expect(args).To(Equal([]string{"ffmpeg", "-i", "file.mp3", "-f", "mp3", "-ar", "48000", "-"}))
+		})
+
+		It("appends when no trailing dash", func() {
+			args := injectBeforeOutput([]string{"ffmpeg", "-i", "file.mp3"}, "-ar", "48000")
+			Expect(args).To(Equal([]string{"ffmpeg", "-i", "file.mp3", "-ar", "48000"}))
+		})
+	})
+
 	Describe("FFmpeg", func() {
 		Context("when FFmpeg is available", func() {
 			var ff FFmpeg
@@ -93,7 +381,12 @@ var _ = Describe("ffmpeg", func() {
 				command := "ffmpeg -f lavfi -i sine=frequency=1000:duration=0 -f mp3 -"
 
 				// The input file is not used here, but we need to provide a valid path to the Transcode function
-				stream, err := ff.Transcode(ctx, command, "tests/fixtures/test.mp3", 128, 0)
+				stream, err := ff.Transcode(ctx, TranscodeOptions{
+					Command:  command,
+					Format:   "mp3",
+					FilePath: "tests/fixtures/test.mp3",
+					BitRate:  128,
+				})
 				Expect(err).ToNot(HaveOccurred())
 				defer stream.Close()
 
@@ -115,7 +408,12 @@ var _ = Describe("ffmpeg", func() {
 				cancel() // Cancel immediately
 
 				// This should fail immediately
-				_, err := ff.Transcode(ctx, "ffmpeg -i %s -f mp3 -", "tests/fixtures/test.mp3", 128, 0)
+				_, err := ff.Transcode(ctx, TranscodeOptions{
+					Command:  "ffmpeg -i %s -f mp3 -",
+					Format:   "mp3",
+					FilePath: "tests/fixtures/test.mp3",
+					BitRate:  128,
+				})
 				Expect(err).To(MatchError(context.Canceled))
 			})
 		})
@@ -142,7 +440,10 @@ var _ = Describe("ffmpeg", func() {
 				defer cancel()
 
 				// Start a process that will run for a while
-				stream, err := ff.Transcode(ctx, longRunningCmd, "tests/fixtures/test.mp3", 0, 0)
+				stream, err := ff.Transcode(ctx, TranscodeOptions{
+					Command:  longRunningCmd,
+					FilePath: "tests/fixtures/test.mp3",
+				})
 				Expect(err).ToNot(HaveOccurred())
 				defer stream.Close()
 

core/media_streamer.go

@@ -18,9 +18,20 @@ import (
 	"github.com/navidrome/navidrome/utils/cache"
 )
 
+// StreamRequest contains all parameters for creating a media stream.
+type StreamRequest struct {
+	ID         string
+	Format     string
+	BitRate    int // kbps
+	SampleRate int
+	BitDepth   int
+	Channels   int
+	Offset     int // seconds
+}
+
 type MediaStreamer interface {
-	NewStream(ctx context.Context, id string, reqFormat string, reqBitRate int, offset int) (*Stream, error)
+	NewStream(ctx context.Context, req StreamRequest) (*Stream, error)
-	DoStream(ctx context.Context, mf *model.MediaFile, reqFormat string, reqBitRate int, reqOffset int) (*Stream, error)
+	DoStream(ctx context.Context, mf *model.MediaFile, req StreamRequest) (*Stream, error)
 }
 
 type TranscodingCache cache.FileCache
@@ -41,39 +52,43 @@ type streamJob struct {
 	filePath   string
 	format     string
 	bitRate    int
+	sampleRate int
+	bitDepth   int
+	channels   int
 	offset     int
 }
 
 func (j *streamJob) Key() string {
-	return fmt.Sprintf("%s.%s.%d.%s.%d", j.mf.ID, j.mf.UpdatedAt.Format(time.RFC3339Nano), j.bitRate, j.format, j.offset)
+	return fmt.Sprintf("%s.%s.%d.%d.%d.%d.%s.%d", j.mf.ID, j.mf.UpdatedAt.Format(time.RFC3339Nano), j.bitRate, j.sampleRate, j.bitDepth, j.channels, j.format, j.offset)
 }
 
-func (ms *mediaStreamer) NewStream(ctx context.Context, id string, reqFormat string, reqBitRate int, reqOffset int) (*Stream, error) {
+func (ms *mediaStreamer) NewStream(ctx context.Context, req StreamRequest) (*Stream, error) {
-	mf, err := ms.ds.MediaFile(ctx).Get(id)
+	mf, err := ms.ds.MediaFile(ctx).Get(req.ID)
 	if err != nil {
 		return nil, err
 	}
 
-	return ms.DoStream(ctx, mf, reqFormat, reqBitRate, reqOffset)
+	return ms.DoStream(ctx, mf, req)
 }
 
-func (ms *mediaStreamer) DoStream(ctx context.Context, mf *model.MediaFile, reqFormat string, reqBitRate int, reqOffset int) (*Stream, error) {
+func (ms *mediaStreamer) DoStream(ctx context.Context, mf *model.MediaFile, req StreamRequest) (*Stream, error) {
 	var format string
 	var bitRate int
 	var cached bool
 	defer func() {
 		log.Info(ctx, "Streaming file", "title", mf.Title, "artist", mf.Artist, "format", format, "cached", cached,
-			"bitRate", bitRate, "user", userName(ctx), "transcoding", format != "raw",
+			"bitRate", bitRate, "sampleRate", req.SampleRate, "bitDepth", req.BitDepth, "channels", req.Channels,
+			"user", userName(ctx), "transcoding", format != "raw",
 			"originalFormat", mf.Suffix, "originalBitRate", mf.BitRate)
 	}()
 
-	format, bitRate = selectTranscodingOptions(ctx, ms.ds, mf, reqFormat, reqBitRate)
+	format, bitRate = selectTranscodingOptions(ctx, ms.ds, mf, req.Format, req.BitRate, req.SampleRate)
 	s := &Stream{ctx: ctx, mf: mf, format: format, bitRate: bitRate}
 	filePath := mf.AbsolutePath()
 
 	if format == "raw" {
 		log.Debug(ctx, "Streaming RAW file", "id", mf.ID, "path", filePath,
-			"requestBitrate", reqBitRate, "requestFormat", reqFormat, "requestOffset", reqOffset,
+			"requestBitrate", req.BitRate, "requestFormat", req.Format, "requestOffset", req.Offset,
 			"originalBitrate", mf.BitRate, "originalFormat", mf.Suffix,
 			"selectedBitrate", bitRate, "selectedFormat", format)
 		f, err := os.Open(filePath)
@@ -92,7 +107,10 @@ func (ms *mediaStreamer) DoStream(ctx context.Context, mf *model.MediaFile, reqF
 		filePath:   filePath,
 		format:     format,
 		bitRate:    bitRate,
-		offset:   reqOffset,
+		sampleRate: req.SampleRate,
+		bitDepth:   req.BitDepth,
+		channels:   req.Channels,
+		offset:     req.Offset,
 	}
 	r, err := ms.cache.Get(ctx, job)
 	if err != nil {
@@ -105,7 +123,7 @@ func (ms *mediaStreamer) DoStream(ctx context.Context, mf *model.MediaFile, reqF
 	s.Seeker = r.Seeker
 
 	log.Debug(ctx, "Streaming TRANSCODED file", "id", mf.ID, "path", filePath,
-		"requestBitrate", reqBitRate, "requestFormat", reqFormat, "requestOffset", reqOffset,
+		"requestBitrate", req.BitRate, "requestFormat", req.Format, "requestOffset", req.Offset,
 		"originalBitrate", mf.BitRate, "originalFormat", mf.Suffix,
 		"selectedBitrate", bitRate, "selectedFormat", format, "cached", cached, "seekable", s.Seekable())
 
@@ -131,12 +149,13 @@ func (s *Stream) EstimatedContentLength() int {
 }
 
 // TODO This function deserves some love (refactoring)
-func selectTranscodingOptions(ctx context.Context, ds model.DataStore, mf *model.MediaFile, reqFormat string, reqBitRate int) (format string, bitRate int) {
+func selectTranscodingOptions(ctx context.Context, ds model.DataStore, mf *model.MediaFile, reqFormat string, reqBitRate int, reqSampleRate int) (format string, bitRate int) {
 	format = "raw"
 	if reqFormat == "raw" {
 		return format, 0
 	}
-	if reqFormat == mf.Suffix && reqBitRate == 0 {
+	needsResample := reqSampleRate > 0 && reqSampleRate < mf.SampleRate
+	if reqFormat == mf.Suffix && reqBitRate == 0 && !needsResample {
 		bitRate = mf.BitRate
 		return format, bitRate
 	}
@@ -175,7 +194,7 @@ func selectTranscodingOptions(ctx context.Context, ds model.DataStore, mf *model
 			bitRate = t.DefaultBitRate
 		}
 	}
-	if format == mf.Suffix && bitRate >= mf.BitRate {
+	if format == mf.Suffix && bitRate >= mf.BitRate && !needsResample {
 		format = "raw"
 		bitRate = 0
 	}
@@ -217,7 +236,16 @@ func NewTranscodingCache() TranscodingCache {
 				transcodingCtx = request.AddValues(context.Background(), ctx)
 			}
 
-			out, err := job.ms.transcoder.Transcode(transcodingCtx, t.Command, job.filePath, job.bitRate, job.offset)
+			out, err := job.ms.transcoder.Transcode(transcodingCtx, ffmpeg.TranscodeOptions{
+				Command:    t.Command,
+				Format:     job.format,
+				FilePath:   job.filePath,
+				BitRate:    job.bitRate,
+				SampleRate: job.sampleRate,
+				BitDepth:   job.bitDepth,
+				Channels:   job.channels,
+				Offset:     job.offset,
+			})
 			if err != nil {
 				log.Error(ctx, "Error starting transcoder", "id", job.mf.ID, err)
 				return nil, os.ErrInvalid

core/media_streamer_Internal_test.go

@@ -26,42 +26,64 @@ var _ = Describe("MediaStreamer", func() {
 			It("returns raw if raw is requested", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, _ := selectTranscodingOptions(ctx, ds, mf, "raw", 0)
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "raw", 0, 0)
 				Expect(format).To(Equal("raw"))
 			})
 			It("returns raw if a transcoder does not exists", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, _ := selectTranscodingOptions(ctx, ds, mf, "m4a", 0)
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "m4a", 0, 0)
 				Expect(format).To(Equal("raw"))
 			})
 			It("returns the requested format if a transcoder exists", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0, 0)
 				Expect(format).To(Equal("mp3"))
 				Expect(bitRate).To(Equal(160)) // Default Bit Rate
 			})
 			It("returns raw if requested format is the same as the original and it is not necessary to downsample", func() {
 				mf.Suffix = "mp3"
 				mf.BitRate = 112
-				format, _ := selectTranscodingOptions(ctx, ds, mf, "mp3", 128)
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "mp3", 128, 0)
 				Expect(format).To(Equal("raw"))
 			})
 			It("returns the requested format if requested BitRate is lower than original", func() {
 				mf.Suffix = "mp3"
 				mf.BitRate = 320
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 192)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 192, 0)
 				Expect(format).To(Equal("mp3"))
 				Expect(bitRate).To(Equal(192))
 			})
 			It("returns raw if requested format is the same as the original, but requested BitRate is 0", func() {
 				mf.Suffix = "mp3"
 				mf.BitRate = 320
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0, 0)
 				Expect(format).To(Equal("raw"))
 				Expect(bitRate).To(Equal(320))
 			})
+			It("returns the format when same format is requested but with a lower sample rate", func() {
+				mf.Suffix = "flac"
+				mf.BitRate = 2118
+				mf.SampleRate = 96000
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "flac", 0, 48000)
+				Expect(format).To(Equal("flac"))
+				Expect(bitRate).To(Equal(0))
+			})
+			It("returns raw when same format is requested with same sample rate", func() {
+				mf.Suffix = "flac"
+				mf.BitRate = 1000
+				mf.SampleRate = 48000
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "flac", 0, 48000)
+				Expect(format).To(Equal("raw"))
+			})
+			It("returns raw when same format is requested with no sample rate constraint", func() {
+				mf.Suffix = "flac"
+				mf.BitRate = 1000
+				mf.SampleRate = 96000
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "flac", 0, 0)
+				Expect(format).To(Equal("raw"))
+			})
 			Context("Downsampling", func() {
 				BeforeEach(func() {
 					conf.Server.DefaultDownsamplingFormat = "opus"
@@ -69,13 +91,13 @@ var _ = Describe("MediaStreamer", func() {
 					mf.BitRate = 960
 				})
 				It("returns the DefaultDownsamplingFormat if a maxBitrate is requested but not the format", func() {
-					format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 128)
+					format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 128, 0)
 					Expect(format).To(Equal("opus"))
 					Expect(bitRate).To(Equal(128))
 				})
 				It("returns raw if maxBitrate is equal or greater than original", func() {
 					// This happens with DSub (and maybe other clients?). See https://github.com/navidrome/navidrome/issues/2066
-					format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 960)
+					format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 960, 0)
 					Expect(format).To(Equal("raw"))
 					Expect(bitRate).To(Equal(0))
 				})
@@ -90,34 +112,34 @@ var _ = Describe("MediaStreamer", func() {
 			It("returns raw if raw is requested", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, _ := selectTranscodingOptions(ctx, ds, mf, "raw", 0)
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "raw", 0, 0)
 				Expect(format).To(Equal("raw"))
 			})
 			It("returns configured format/bitrate as default", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 0)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 0, 0)
 				Expect(format).To(Equal("oga"))
 				Expect(bitRate).To(Equal(96))
 			})
 			It("returns requested format", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0, 0)
 				Expect(format).To(Equal("mp3"))
 				Expect(bitRate).To(Equal(160)) // Default Bit Rate
 			})
 			It("returns requested bitrate", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 80)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 80, 0)
 				Expect(format).To(Equal("oga"))
 				Expect(bitRate).To(Equal(80))
 			})
 			It("returns raw if selected bitrate and format is the same as original", func() {
 				mf.Suffix = "mp3"
 				mf.BitRate = 192
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 192)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 192, 0)
 				Expect(format).To(Equal("raw"))
 				Expect(bitRate).To(Equal(0))
 			})
@@ -133,27 +155,27 @@ var _ = Describe("MediaStreamer", func() {
 			It("returns raw if raw is requested", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, _ := selectTranscodingOptions(ctx, ds, mf, "raw", 0)
+				format, _ := selectTranscodingOptions(ctx, ds, mf, "raw", 0, 0)
 				Expect(format).To(Equal("raw"))
 			})
 			It("returns configured format/bitrate as default", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 0)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 0, 0)
 				Expect(format).To(Equal("oga"))
 				Expect(bitRate).To(Equal(192))
 			})
 			It("returns requested format", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "mp3", 0, 0)
 				Expect(format).To(Equal("mp3"))
 				Expect(bitRate).To(Equal(160)) // Default Bit Rate
 			})
 			It("returns requested bitrate", func() {
 				mf.Suffix = "flac"
 				mf.BitRate = 1000
-				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 160)
+				format, bitRate := selectTranscodingOptions(ctx, ds, mf, "", 160, 0)
 				Expect(format).To(Equal("oga"))
 				Expect(bitRate).To(Equal(160))
 			})

core/media_streamer_test.go

@@ -39,34 +39,34 @@ var _ = Describe("MediaStreamer", func() {
 
 	Context("NewStream", func() {
 		It("returns a seekable stream if format is 'raw'", func() {
-			s, err := streamer.NewStream(ctx, "123", "raw", 0, 0)
+			s, err := streamer.NewStream(ctx, core.StreamRequest{ID: "123", Format: "raw"})
 			Expect(err).ToNot(HaveOccurred())
 			Expect(s.Seekable()).To(BeTrue())
 		})
 		It("returns a seekable stream if maxBitRate is 0", func() {
-			s, err := streamer.NewStream(ctx, "123", "mp3", 0, 0)
+			s, err := streamer.NewStream(ctx, core.StreamRequest{ID: "123", Format: "mp3"})
 			Expect(err).ToNot(HaveOccurred())
 			Expect(s.Seekable()).To(BeTrue())
 		})
 		It("returns a seekable stream if maxBitRate is higher than file bitRate", func() {
-			s, err := streamer.NewStream(ctx, "123", "mp3", 320, 0)
+			s, err := streamer.NewStream(ctx, core.StreamRequest{ID: "123", Format: "mp3", BitRate: 320})
 			Expect(err).ToNot(HaveOccurred())
 			Expect(s.Seekable()).To(BeTrue())
 		})
 		It("returns a NON seekable stream if transcode is required", func() {
-			s, err := streamer.NewStream(ctx, "123", "mp3", 64, 0)
+			s, err := streamer.NewStream(ctx, core.StreamRequest{ID: "123", Format: "mp3", BitRate: 64})
 			Expect(err).To(BeNil())
 			Expect(s.Seekable()).To(BeFalse())
 			Expect(s.Duration()).To(Equal(float32(257.0)))
 		})
 		It("returns a seekable stream if the file is complete in the cache", func() {
-			s, err := streamer.NewStream(ctx, "123", "mp3", 32, 0)
+			s, err := streamer.NewStream(ctx, core.StreamRequest{ID: "123", Format: "mp3", BitRate: 32})
 			Expect(err).To(BeNil())
 			_, _ = io.ReadAll(s)
 			_ = s.Close()
 			Eventually(func() bool { return ffmpeg.IsClosed() }, "3s").Should(BeTrue())
 
-			s, err = streamer.NewStream(ctx, "123", "mp3", 32, 0)
+			s, err = streamer.NewStream(ctx, core.StreamRequest{ID: "123", Format: "mp3", BitRate: 32})
 			Expect(err).To(BeNil())
 			Expect(s.Seekable()).To(BeTrue())
 		})

core/transcode/aliases.go

@@ -0,0 +1,87 @@
+package transcode
+
+import (
+	"slices"
+	"strings"
+)
+
+// containerAliasGroups maps each container alias to a canonical group name.
+var containerAliasGroups = func() map[string]string {
+	groups := [][]string{
+		{"aac", "adts", "m4a", "mp4", "m4b", "m4p"},
+		{"mpeg", "mp3", "mp2"},
+		{"ogg", "oga"},
+		{"aif", "aiff"},
+		{"asf", "wma"},
+		{"mpc", "mpp"},
+		{"wv"},
+	}
+	m := make(map[string]string)
+	for _, g := range groups {
+		canonical := g[0]
+		for _, name := range g {
+			m[name] = canonical
+		}
+	}
+	return m
+}()
+
+// codecAliasGroups maps each codec alias to a canonical group name.
+// Codecs within the same group are considered equivalent.
+var codecAliasGroups = func() map[string]string {
+	groups := [][]string{
+		{"aac", "adts"},
+		{"ac3", "ac-3"},
+		{"eac3", "e-ac3", "e-ac-3", "eac-3"},
+		{"mpc7", "musepack7"},
+		{"mpc8", "musepack8"},
+		{"wma1", "wmav1"},
+		{"wma2", "wmav2"},
+		{"wmalossless", "wma9lossless"},
+		{"wmapro", "wma9pro"},
+		{"shn", "shorten"},
+		{"mp4als", "als"},
+	}
+	m := make(map[string]string)
+	for _, g := range groups {
+		for _, name := range g {
+			m[name] = g[0] // canonical = first entry
+		}
+	}
+	return m
+}()
+
+// matchesWithAliases checks if a value matches any entry in candidates,
+// consulting the alias map for equivalent names.
+func matchesWithAliases(value string, candidates []string, aliases map[string]string) bool {
+	value = strings.ToLower(value)
+	canonical := aliases[value]
+	for _, c := range candidates {
+		c = strings.ToLower(c)
+		if c == value {
+			return true
+		}
+		if canonical != "" && aliases[c] == canonical {
+			return true
+		}
+	}
+	return false
+}
+
+// matchesContainer checks if a file suffix matches any of the container names,
+// including common aliases.
+func matchesContainer(suffix string, containers []string) bool {
+	return matchesWithAliases(suffix, containers, containerAliasGroups)
+}
+
+// matchesCodec checks if a codec matches any of the codec names,
+// including common aliases.
+func matchesCodec(codec string, codecs []string) bool {
+	return matchesWithAliases(codec, codecs, codecAliasGroups)
+}
+
+func containsIgnoreCase(slice []string, s string) bool {
+	return slices.ContainsFunc(slice, func(item string) bool {
+		return strings.EqualFold(item, s)
+	})
+}

core/transcode/codec.go

@@ -0,0 +1,59 @@
+package transcode
+
+import "strings"
+
+// isLosslessFormat returns true if the format is a lossless audio codec/format.
+// Note: core/ffmpeg has a separate isLosslessOutputFormat that covers only formats
+// ffmpeg can produce as output (a smaller set). This function covers all known lossless formats
+// for transcoding decision purposes.
+func isLosslessFormat(format string) bool {
+	switch strings.ToLower(format) {
+	case "flac", "alac", "wav", "aiff", "ape", "wv", "tta", "tak", "shn", "dsd", "pcm":
+		return true
+	}
+	return false
+}
+
+// normalizeSourceSampleRate adjusts the source sample rate for codecs that store
+// it differently than PCM. Currently handles DSD (÷8):
+// DSD64=2822400→352800, DSD128=5644800→705600, etc.
+// For other codecs, returns the rate unchanged.
+func normalizeSourceSampleRate(sampleRate int, codec string) int {
+	if strings.EqualFold(codec, "dsd") && sampleRate > 0 {
+		return sampleRate / 8
+	}
+	return sampleRate
+}
+
+// normalizeSourceBitDepth adjusts the source bit depth for codecs that use
+// non-standard bit depths. Currently handles DSD (1-bit → 24-bit PCM, which is
+// what ffmpeg produces). For other codecs, returns the depth unchanged.
+func normalizeSourceBitDepth(bitDepth int, codec string) int {
+	if strings.EqualFold(codec, "dsd") && bitDepth == 1 {
+		return 24
+	}
+	return bitDepth
+}
+
+// codecFixedOutputSampleRate returns the mandatory output sample rate for codecs
+// that always resample regardless of input (e.g., Opus always outputs 48000Hz).
+// Returns 0 if the codec has no fixed output rate.
+func codecFixedOutputSampleRate(codec string) int {
+	switch strings.ToLower(codec) {
+	case "opus":
+		return 48000
+	}
+	return 0
+}
+
+// codecMaxSampleRate returns the hard maximum output sample rate for a codec.
+// Returns 0 if the codec has no hard limit.
+func codecMaxSampleRate(codec string) int {
+	switch strings.ToLower(codec) {
+	case "mp3":
+		return 48000
+	case "aac":
+		return 96000
+	}
+	return 0
+}

core/transcode/limitations.go

@@ -0,0 +1,206 @@
+package transcode
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/navidrome/navidrome/model"
+)
+
+// adjustResult represents the outcome of applying a limitation to a transcoded stream value
+type adjustResult int
+
+const (
+	adjustNone      adjustResult = iota // Value already satisfies the limitation
+	adjustAdjusted                      // Value was changed to fit the limitation
+	adjustCannotFit                     // Cannot satisfy the limitation (reject this profile)
+)
+
+// checkLimitations checks codec profile limitations against source media.
+// Returns "" if all limitations pass, or a typed reason string for the first failure.
+func checkLimitations(mf *model.MediaFile, sourceBitrate int, limitations []Limitation) string {
+	for _, lim := range limitations {
+		var ok bool
+		var reason string
+
+		switch lim.Name {
+		case LimitationAudioChannels:
+			ok = checkIntLimitation(mf.Channels, lim.Comparison, lim.Values)
+			reason = "audio channels not supported"
+		case LimitationAudioSamplerate:
+			ok = checkIntLimitation(mf.SampleRate, lim.Comparison, lim.Values)
+			reason = "audio samplerate not supported"
+		case LimitationAudioBitrate:
+			ok = checkIntLimitation(sourceBitrate, lim.Comparison, lim.Values)
+			reason = "audio bitrate not supported"
+		case LimitationAudioBitdepth:
+			ok = checkIntLimitation(mf.BitDepth, lim.Comparison, lim.Values)
+			reason = "audio bitdepth not supported"
+		case LimitationAudioProfile:
+			// TODO: populate source profile when MediaFile has audio profile info
+			ok = checkStringLimitation("", lim.Comparison, lim.Values)
+			reason = "audio profile not supported"
+		default:
+			continue
+		}
+
+		if !ok && lim.Required {
+			return reason
+		}
+	}
+	return ""
+}
+
+// applyLimitation adjusts a transcoded stream parameter to satisfy the limitation.
+// Returns the adjustment result.
+func applyLimitation(sourceBitrate int, lim *Limitation, ts *StreamDetails) adjustResult {
+	switch lim.Name {
+	case LimitationAudioChannels:
+		return applyIntLimitation(lim.Comparison, lim.Values, ts.Channels, func(v int) { ts.Channels = v })
+	case LimitationAudioBitrate:
+		current := ts.Bitrate
+		if current == 0 {
+			current = sourceBitrate
+		}
+		return applyIntLimitation(lim.Comparison, lim.Values, current, func(v int) { ts.Bitrate = v })
+	case LimitationAudioSamplerate:
+		return applyIntLimitation(lim.Comparison, lim.Values, ts.SampleRate, func(v int) { ts.SampleRate = v })
+	case LimitationAudioBitdepth:
+		if ts.BitDepth > 0 {
+			return applyIntLimitation(lim.Comparison, lim.Values, ts.BitDepth, func(v int) { ts.BitDepth = v })
+		}
+	case LimitationAudioProfile:
+		// TODO: implement when audio profile data is available
+	}
+	return adjustNone
+}
+
+// applyIntLimitation applies a limitation comparison to a value.
+// If the value needs adjusting, calls the setter and returns the result.
+func applyIntLimitation(comparison string, values []string, current int, setter func(int)) adjustResult {
+	if len(values) == 0 {
+		return adjustNone
+	}
+
+	switch comparison {
+	case ComparisonLessThanEqual:
+		limit, ok := parseInt(values[0])
+		if !ok {
+			return adjustNone
+		}
+		if current <= limit {
+			return adjustNone
+		}
+		setter(limit)
+		return adjustAdjusted
+	case ComparisonGreaterThanEqual:
+		limit, ok := parseInt(values[0])
+		if !ok {
+			return adjustNone
+		}
+		if current >= limit {
+			return adjustNone
+		}
+		// Cannot upscale
+		return adjustCannotFit
+	case ComparisonEquals:
+		// Check if current value matches any allowed value
+		for _, v := range values {
+			if limit, ok := parseInt(v); ok && current == limit {
+				return adjustNone
+			}
+		}
+		// Find the closest allowed value below current (don't upscale)
+		var closest int
+		found := false
+		for _, v := range values {
+			if limit, ok := parseInt(v); ok && limit < current {
+				if !found || limit > closest {
+					closest = limit
+					found = true
+				}
+			}
+		}
+		if found {
+			setter(closest)
+			return adjustAdjusted
+		}
+		return adjustCannotFit
+	case ComparisonNotEquals:
+		for _, v := range values {
+			if limit, ok := parseInt(v); ok && current == limit {
+				return adjustCannotFit
+			}
+		}
+		return adjustNone
+	}
+
+	return adjustNone
+}
+
+func checkIntLimitation(value int, comparison string, values []string) bool {
+	if len(values) == 0 {
+		return true
+	}
+
+	switch comparison {
+	case ComparisonLessThanEqual:
+		limit, ok := parseInt(values[0])
+		if !ok {
+			return true
+		}
+		return value <= limit
+	case ComparisonGreaterThanEqual:
+		limit, ok := parseInt(values[0])
+		if !ok {
+			return true
+		}
+		return value >= limit
+	case ComparisonEquals:
+		for _, v := range values {
+			if limit, ok := parseInt(v); ok && value == limit {
+				return true
+			}
+		}
+		return false
+	case ComparisonNotEquals:
+		for _, v := range values {
+			if limit, ok := parseInt(v); ok && value == limit {
+				return false
+			}
+		}
+		return true
+	}
+	return true
+}
+
+// checkStringLimitation checks a string value against a limitation.
+// Only Equals and NotEquals comparisons are meaningful for strings.
+// LessThanEqual/GreaterThanEqual are not applicable and always pass.
+func checkStringLimitation(value string, comparison string, values []string) bool {
+	switch comparison {
+	case ComparisonEquals:
+		for _, v := range values {
+			if strings.EqualFold(value, v) {
+				return true
+			}
+		}
+		return false
+	case ComparisonNotEquals:
+		for _, v := range values {
+			if strings.EqualFold(value, v) {
+				return false
+			}
+		}
+		return true
+	}
+	return true
+}
+
+func parseInt(s string) (int, bool) {
+	v, err := strconv.Atoi(s)
+	if err != nil || v < 0 {
+		return 0, false
+	}
+	return v, true
+}

core/transcode/transcode.go

@@ -0,0 +1,400 @@
+package transcode
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/navidrome/navidrome/core/auth"
+	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/model"
+)
+
+const (
+	tokenTTL       = 12 * time.Hour
+	defaultBitrate = 256 // kbps
+
+	// JWT claim keys for transcode params tokens
+	claimMediaID    = "mid" // Media file ID
+	claimDirectPlay = "dp"  // Direct play flag (bool)
+	claimUpdatedAt  = "ua"  // Source file updated-at (Unix seconds)
+	claimFormat     = "fmt" // Target transcoding format
+	claimBitrate    = "br"  // Target bitrate (kbps)
+	claimChannels   = "ch"  // Target channels
+	claimSampleRate = "sr"  // Target sample rate (Hz)
+	claimBitDepth   = "bd"  // Target bit depth
+)
+
+func NewDecider(ds model.DataStore) Decider {
+	return &deciderService{
+		ds: ds,
+	}
+}
+
+type deciderService struct {
+	ds model.DataStore
+}
+
+func (s *deciderService) MakeDecision(ctx context.Context, mf *model.MediaFile, clientInfo *ClientInfo) (*Decision, error) {
+	decision := &Decision{
+		MediaID:         mf.ID,
+		SourceUpdatedAt: mf.UpdatedAt,
+	}
+
+	sourceBitrate := mf.BitRate // kbps
+
+	log.Trace(ctx, "Making transcode decision", "mediaID", mf.ID, "container", mf.Suffix,
+		"codec", mf.AudioCodec(), "bitrate", sourceBitrate, "channels", mf.Channels,
+		"sampleRate", mf.SampleRate, "lossless", mf.IsLossless(), "client", clientInfo.Name)
+
+	// Build source stream details
+	decision.SourceStream = buildSourceStream(mf)
+
+	// Check global bitrate constraint first.
+	if clientInfo.MaxAudioBitrate > 0 && sourceBitrate > clientInfo.MaxAudioBitrate {
+		log.Trace(ctx, "Global bitrate constraint exceeded, skipping direct play",
+			"sourceBitrate", sourceBitrate, "maxAudioBitrate", clientInfo.MaxAudioBitrate)
+		decision.TranscodeReasons = append(decision.TranscodeReasons, "audio bitrate not supported")
+		// Skip direct play profiles entirely — global constraint fails
+	} else {
+		// Try direct play profiles, collecting reasons for each failure
+		for _, profile := range clientInfo.DirectPlayProfiles {
+			if reason := s.checkDirectPlayProfile(mf, sourceBitrate, &profile, clientInfo); reason == "" {
+				decision.CanDirectPlay = true
+				decision.TranscodeReasons = nil // Clear any previously collected reasons
+				break
+			} else {
+				decision.TranscodeReasons = append(decision.TranscodeReasons, reason)
+			}
+		}
+	}
+
+	// If direct play is possible, we're done
+	if decision.CanDirectPlay {
+		log.Debug(ctx, "Transcode decision: direct play", "mediaID", mf.ID, "container", mf.Suffix, "codec", mf.AudioCodec())
+		return decision, nil
+	}
+
+	// Try transcoding profiles (in order of preference)
+	for _, profile := range clientInfo.TranscodingProfiles {
+		if ts, transcodeFormat := s.computeTranscodedStream(ctx, mf, sourceBitrate, &profile, clientInfo); ts != nil {
+			decision.CanTranscode = true
+			decision.TargetFormat = transcodeFormat
+			decision.TargetBitrate = ts.Bitrate
+			decision.TargetChannels = ts.Channels
+			decision.TargetSampleRate = ts.SampleRate
+			decision.TargetBitDepth = ts.BitDepth
+			decision.TranscodeStream = ts
+			break
+		}
+	}
+
+	if decision.CanTranscode {
+		log.Debug(ctx, "Transcode decision: transcode", "mediaID", mf.ID,
+			"targetFormat", decision.TargetFormat, "targetBitrate", decision.TargetBitrate,
+			"targetChannels", decision.TargetChannels, "reasons", decision.TranscodeReasons)
+	}
+
+	// If neither direct play nor transcode is possible
+	if !decision.CanDirectPlay && !decision.CanTranscode {
+		decision.ErrorReason = "no compatible playback profile found"
+		log.Warn(ctx, "Transcode decision: no compatible profile", "mediaID", mf.ID,
+			"container", mf.Suffix, "codec", mf.AudioCodec(), "reasons", decision.TranscodeReasons)
+	}
+
+	return decision, nil
+}
+
+func buildSourceStream(mf *model.MediaFile) StreamDetails {
+	return StreamDetails{
+		Container:  mf.Suffix,
+		Codec:      mf.AudioCodec(),
+		Bitrate:    mf.BitRate,
+		SampleRate: mf.SampleRate,
+		BitDepth:   mf.BitDepth,
+		Channels:   mf.Channels,
+		Duration:   mf.Duration,
+		Size:       mf.Size,
+		IsLossless: mf.IsLossless(),
+	}
+}
+
+// checkDirectPlayProfile returns "" if the profile matches (direct play OK),
+// or a typed reason string if it doesn't match.
+func (s *deciderService) checkDirectPlayProfile(mf *model.MediaFile, sourceBitrate int, profile *DirectPlayProfile, clientInfo *ClientInfo) string {
+	// Check protocol (only http for now)
+	if len(profile.Protocols) > 0 && !containsIgnoreCase(profile.Protocols, ProtocolHTTP) {
+		return "protocol not supported"
+	}
+
+	// Check container
+	if len(profile.Containers) > 0 && !matchesContainer(mf.Suffix, profile.Containers) {
+		return "container not supported"
+	}
+
+	// Check codec
+	if len(profile.AudioCodecs) > 0 && !matchesCodec(mf.AudioCodec(), profile.AudioCodecs) {
+		return "audio codec not supported"
+	}
+
+	// Check channels
+	if profile.MaxAudioChannels > 0 && mf.Channels > profile.MaxAudioChannels {
+		return "audio channels not supported"
+	}
+
+	// Check codec-specific limitations
+	for _, codecProfile := range clientInfo.CodecProfiles {
+		if strings.EqualFold(codecProfile.Type, CodecProfileTypeAudio) && matchesCodec(mf.AudioCodec(), []string{codecProfile.Name}) {
+			if reason := checkLimitations(mf, sourceBitrate, codecProfile.Limitations); reason != "" {
+				return reason
+			}
+		}
+	}
+
+	return ""
+}
+
+// computeTranscodedStream attempts to build a valid transcoded stream for the given profile.
+// Returns the stream details and the internal transcoding format (which may differ from the
+// response container when a codec fallback occurs, e.g., "mp4"→"aac").
+// Returns nil, "" if the profile cannot produce a valid output.
+func (s *deciderService) computeTranscodedStream(ctx context.Context, mf *model.MediaFile, sourceBitrate int, profile *Profile, clientInfo *ClientInfo) (*StreamDetails, string) {
+	// Check protocol (only http for now)
+	if profile.Protocol != "" && !strings.EqualFold(profile.Protocol, ProtocolHTTP) {
+		log.Trace(ctx, "Skipping transcoding profile: unsupported protocol", "protocol", profile.Protocol)
+		return nil, ""
+	}
+
+	responseContainer, targetFormat := s.resolveTargetFormat(ctx, profile)
+	if targetFormat == "" {
+		return nil, ""
+	}
+
+	targetIsLossless := isLosslessFormat(targetFormat)
+
+	// Reject lossy to lossless conversion
+	if !mf.IsLossless() && targetIsLossless {
+		log.Trace(ctx, "Skipping transcoding profile: lossy to lossless not allowed", "targetFormat", targetFormat)
+		return nil, ""
+	}
+
+	ts := &StreamDetails{
+		Container:  responseContainer,
+		Codec:      strings.ToLower(profile.AudioCodec),
+		SampleRate: normalizeSourceSampleRate(mf.SampleRate, mf.AudioCodec()),
+		Channels:   mf.Channels,
+		BitDepth:   normalizeSourceBitDepth(mf.BitDepth, mf.AudioCodec()),
+		IsLossless: targetIsLossless,
+	}
+	if ts.Codec == "" {
+		ts.Codec = targetFormat
+	}
+
+	// Apply codec-intrinsic sample rate adjustments before codec profile limitations
+	if fixedRate := codecFixedOutputSampleRate(ts.Codec); fixedRate > 0 {
+		ts.SampleRate = fixedRate
+	}
+	if maxRate := codecMaxSampleRate(ts.Codec); maxRate > 0 && ts.SampleRate > maxRate {
+		ts.SampleRate = maxRate
+	}
+
+	// Determine target bitrate (all in kbps)
+	if ok := s.computeBitrate(ctx, mf, sourceBitrate, targetFormat, targetIsLossless, clientInfo, ts); !ok {
+		return nil, ""
+	}
+
+	// Apply MaxAudioChannels from the transcoding profile
+	if profile.MaxAudioChannels > 0 && mf.Channels > profile.MaxAudioChannels {
+		ts.Channels = profile.MaxAudioChannels
+	}
+
+	// Apply codec profile limitations to the TARGET codec
+	if ok := s.applyCodecLimitations(ctx, sourceBitrate, targetFormat, targetIsLossless, clientInfo, ts); !ok {
+		return nil, ""
+	}
+
+	return ts, targetFormat
+}
+
+// resolveTargetFormat determines the response container and internal target format
+// by looking up transcoding configs. Returns ("", "") if no config found.
+func (s *deciderService) resolveTargetFormat(ctx context.Context, profile *Profile) (responseContainer, targetFormat string) {
+	responseContainer = strings.ToLower(profile.Container)
+	targetFormat = responseContainer
+	if targetFormat == "" {
+		targetFormat = strings.ToLower(profile.AudioCodec)
+		responseContainer = targetFormat
+	}
+
+	// Try the container first, then fall back to the audioCodec (e.g. "ogg" → "opus", "mp4" → "aac").
+	_, err := s.ds.Transcoding(ctx).FindByFormat(targetFormat)
+	if errors.Is(err, model.ErrNotFound) && profile.AudioCodec != "" && !strings.EqualFold(targetFormat, profile.AudioCodec) {
+		codec := strings.ToLower(profile.AudioCodec)
+		log.Trace(ctx, "No transcoding config for container, trying audioCodec", "container", targetFormat, "audioCodec", codec)
+		_, err = s.ds.Transcoding(ctx).FindByFormat(codec)
+		if err == nil {
+			targetFormat = codec
+		}
+	}
+	if err != nil {
+		if !errors.Is(err, model.ErrNotFound) {
+			log.Error(ctx, "Error looking up transcoding config", "format", targetFormat, err)
+		} else {
+			log.Trace(ctx, "Skipping transcoding profile: no transcoding config", "targetFormat", targetFormat)
+		}
+		return "", ""
+	}
+	return responseContainer, targetFormat
+}
+
+// computeBitrate determines the target bitrate for the transcoded stream.
+// Returns false if the profile should be rejected.
+func (s *deciderService) computeBitrate(ctx context.Context, mf *model.MediaFile, sourceBitrate int, targetFormat string, targetIsLossless bool, clientInfo *ClientInfo, ts *StreamDetails) bool {
+	if mf.IsLossless() {
+		if !targetIsLossless {
+			if clientInfo.MaxTranscodingAudioBitrate > 0 {
+				ts.Bitrate = clientInfo.MaxTranscodingAudioBitrate
+			} else {
+				ts.Bitrate = defaultBitrate
+			}
+		} else {
+			if clientInfo.MaxAudioBitrate > 0 && sourceBitrate > clientInfo.MaxAudioBitrate {
+				log.Trace(ctx, "Skipping transcoding profile: lossless target exceeds bitrate limit",
+					"targetFormat", targetFormat, "sourceBitrate", sourceBitrate, "maxAudioBitrate", clientInfo.MaxAudioBitrate)
+				return false
+			}
+		}
+	} else {
+		ts.Bitrate = sourceBitrate
+	}
+
+	// Apply maxAudioBitrate as final cap
+	if clientInfo.MaxAudioBitrate > 0 && ts.Bitrate > 0 && ts.Bitrate > clientInfo.MaxAudioBitrate {
+		ts.Bitrate = clientInfo.MaxAudioBitrate
+	}
+	return true
+}
+
+// applyCodecLimitations applies codec profile limitations to the transcoded stream.
+// Returns false if the profile should be rejected.
+func (s *deciderService) applyCodecLimitations(ctx context.Context, sourceBitrate int, targetFormat string, targetIsLossless bool, clientInfo *ClientInfo, ts *StreamDetails) bool {
+	targetCodec := ts.Codec
+	for _, codecProfile := range clientInfo.CodecProfiles {
+		if !strings.EqualFold(codecProfile.Type, CodecProfileTypeAudio) {
+			continue
+		}
+		if !matchesCodec(targetCodec, []string{codecProfile.Name}) {
+			continue
+		}
+		for _, lim := range codecProfile.Limitations {
+			result := applyLimitation(sourceBitrate, &lim, ts)
+			if strings.EqualFold(lim.Name, LimitationAudioBitrate) && targetIsLossless && result == adjustAdjusted {
+				log.Trace(ctx, "Skipping transcoding profile: cannot adjust bitrate for lossless target",
+					"targetFormat", targetFormat, "codec", targetCodec, "limitation", lim.Name)
+				return false
+			}
+			if result == adjustCannotFit {
+				log.Trace(ctx, "Skipping transcoding profile: codec limitation cannot be satisfied",
+					"targetFormat", targetFormat, "codec", targetCodec, "limitation", lim.Name,
+					"comparison", lim.Comparison, "values", lim.Values)
+				return false
+			}
+		}
+	}
+	return true
+}
+
+func (s *deciderService) CreateTranscodeParams(decision *Decision) (string, error) {
+	exp := time.Now().Add(tokenTTL)
+	claims := map[string]any{
+		claimMediaID:    decision.MediaID,
+		claimDirectPlay: decision.CanDirectPlay,
+		claimUpdatedAt:  decision.SourceUpdatedAt.Truncate(time.Second).Unix(),
+	}
+	if decision.CanTranscode && decision.TargetFormat != "" {
+		claims[claimFormat] = decision.TargetFormat
+		claims[claimBitrate] = decision.TargetBitrate
+		if decision.TargetChannels > 0 {
+			claims[claimChannels] = decision.TargetChannels
+		}
+		if decision.TargetSampleRate > 0 {
+			claims[claimSampleRate] = decision.TargetSampleRate
+		}
+		if decision.TargetBitDepth > 0 {
+			claims[claimBitDepth] = decision.TargetBitDepth
+		}
+	}
+	return auth.CreateExpiringPublicToken(exp, claims)
+}
+
+func (s *deciderService) ParseTranscodeParams(token string) (*Params, error) {
+	claims, err := auth.Validate(token)
+	if err != nil {
+		return nil, err
+	}
+
+	params := &Params{}
+
+	// Required claims
+	mid, ok := claims[claimMediaID].(string)
+	if !ok || mid == "" {
+		return nil, fmt.Errorf("%w: invalid transcode token: missing media ID", ErrTokenInvalid)
+	}
+	params.MediaID = mid
+
+	dp, ok := claims[claimDirectPlay].(bool)
+	if !ok {
+		return nil, fmt.Errorf("%w: invalid transcode token: missing direct play flag", ErrTokenInvalid)
+	}
+	params.DirectPlay = dp
+
+	// Optional claims (legitimately absent for direct-play tokens)
+	if f, ok := claims[claimFormat].(string); ok {
+		params.TargetFormat = f
+	}
+	if br, ok := claims[claimBitrate].(float64); ok {
+		params.TargetBitrate = int(br)
+	}
+	if ch, ok := claims[claimChannels].(float64); ok {
+		params.TargetChannels = int(ch)
+	}
+	if sr, ok := claims[claimSampleRate].(float64); ok {
+		params.TargetSampleRate = int(sr)
+	}
+	if bd, ok := claims[claimBitDepth].(float64); ok {
+		params.TargetBitDepth = int(bd)
+	}
+
+	ua, ok := claims[claimUpdatedAt].(float64)
+	if !ok {
+		return nil, fmt.Errorf("%w: invalid transcode token: missing source timestamp", ErrTokenInvalid)
+	}
+	params.SourceUpdatedAt = time.Unix(int64(ua), 0)
+
+	return params, nil
+}
+
+func (s *deciderService) ValidateTranscodeParams(ctx context.Context, token string, mediaID string) (*Params, *model.MediaFile, error) {
+	params, err := s.ParseTranscodeParams(token)
+	if err != nil {
+		return nil, nil, errors.Join(ErrTokenInvalid, err)
+	}
+	if params.MediaID != mediaID {
+		return nil, nil, fmt.Errorf("%w: token mediaID %q does not match %q", ErrTokenInvalid, params.MediaID, mediaID)
+	}
+	mf, err := s.ds.MediaFile(ctx).Get(mediaID)
+	if err != nil {
+		if errors.Is(err, model.ErrNotFound) {
+			return nil, nil, ErrMediaNotFound
+		}
+		return nil, nil, err
+	}
+	if !mf.UpdatedAt.Truncate(time.Second).Equal(params.SourceUpdatedAt) {
+		log.Info(ctx, "Transcode token is stale", "mediaID", mediaID,
+			"tokenUpdatedAt", params.SourceUpdatedAt, "fileUpdatedAt", mf.UpdatedAt)
+		return nil, nil, ErrTokenStale
+	}
+	return params, mf, nil
+}

core/transcode/transcode_suite_test.go

@@ -0,0 +1,17 @@
+package transcode
+
+import (
+	"testing"
+
+	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/tests"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestTranscode(t *testing.T) {
+	tests.Init(t, false)
+	log.SetLevel(log.LevelFatal)
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Transcode Suite")
+}

core/transcode/types.go

@@ -0,0 +1,140 @@
+package transcode
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/navidrome/navidrome/model"
+)
+
+var (
+	ErrTokenInvalid  = errors.New("invalid or expired transcode token")
+	ErrMediaNotFound = errors.New("media file not found")
+	ErrTokenStale    = errors.New("transcode token is stale: media file has changed")
+)
+
+// Decider is the core service interface for making transcoding decisions
+type Decider interface {
+	MakeDecision(ctx context.Context, mf *model.MediaFile, clientInfo *ClientInfo) (*Decision, error)
+	CreateTranscodeParams(decision *Decision) (string, error)
+	ParseTranscodeParams(token string) (*Params, error)
+	ValidateTranscodeParams(ctx context.Context, token string, mediaID string) (*Params, *model.MediaFile, error)
+}
+
+// ClientInfo represents client playback capabilities.
+// All bitrate values are in kilobits per second (kbps)
+type ClientInfo struct {
+	Name                       string
+	Platform                   string
+	MaxAudioBitrate            int
+	MaxTranscodingAudioBitrate int
+	DirectPlayProfiles         []DirectPlayProfile
+	TranscodingProfiles        []Profile
+	CodecProfiles              []CodecProfile
+}
+
+// DirectPlayProfile describes a format the client can play directly
+type DirectPlayProfile struct {
+	Containers       []string
+	AudioCodecs      []string
+	Protocols        []string
+	MaxAudioChannels int
+}
+
+// Profile describes a transcoding target the client supports
+type Profile struct {
+	Container        string
+	AudioCodec       string
+	Protocol         string
+	MaxAudioChannels int
+}
+
+// CodecProfile describes codec-specific limitations
+type CodecProfile struct {
+	Type        string
+	Name        string
+	Limitations []Limitation
+}
+
+// Limitation describes a specific codec limitation
+type Limitation struct {
+	Name       string
+	Comparison string
+	Values     []string
+	Required   bool
+}
+
+// Protocol values (OpenSubsonic spec enum)
+const (
+	ProtocolHTTP = "http"
+	ProtocolHLS  = "hls"
+)
+
+// Comparison operators (OpenSubsonic spec enum)
+const (
+	ComparisonEquals           = "Equals"
+	ComparisonNotEquals        = "NotEquals"
+	ComparisonLessThanEqual    = "LessThanEqual"
+	ComparisonGreaterThanEqual = "GreaterThanEqual"
+)
+
+// Limitation names (OpenSubsonic spec enum)
+const (
+	LimitationAudioChannels   = "audioChannels"
+	LimitationAudioBitrate    = "audioBitrate"
+	LimitationAudioProfile    = "audioProfile"
+	LimitationAudioSamplerate = "audioSamplerate"
+	LimitationAudioBitdepth   = "audioBitdepth"
+)
+
+// Codec profile types (OpenSubsonic spec enum)
+const (
+	CodecProfileTypeAudio = "AudioCodec"
+)
+
+// Decision represents the internal decision result.
+// All bitrate values are in kilobits per second (kbps).
+type Decision struct {
+	MediaID          string
+	CanDirectPlay    bool
+	CanTranscode     bool
+	TranscodeReasons []string
+	ErrorReason      string
+	TargetFormat     string
+	TargetBitrate    int
+	TargetChannels   int
+	TargetSampleRate int
+	TargetBitDepth   int
+	SourceStream     StreamDetails
+	SourceUpdatedAt  time.Time
+	TranscodeStream  *StreamDetails
+}
+
+// StreamDetails describes audio stream properties.
+// Bitrate is in kilobits per second (kbps).
+type StreamDetails struct {
+	Container  string
+	Codec      string
+	Profile    string // Audio profile (e.g., "LC", "HE-AAC"). Empty until scanner support is added.
+	Bitrate    int
+	SampleRate int
+	BitDepth   int
+	Channels   int
+	Duration   float32
+	Size       int64
+	IsLossless bool
+}
+
+// Params contains the parameters extracted from a transcode token.
+// TargetBitrate is in kilobits per second (kbps).
+type Params struct {
+	MediaID          string
+	DirectPlay       bool
+	TargetFormat     string
+	TargetBitrate    int
+	TargetChannels   int
+	TargetSampleRate int
+	TargetBitDepth   int
+	SourceUpdatedAt  time.Time
+}

core/wire_providers.go

@@ -8,6 +8,7 @@ import (
 	"github.com/navidrome/navidrome/core/metrics"
 	"github.com/navidrome/navidrome/core/playback"
 	"github.com/navidrome/navidrome/core/scrobbler"
+	"github.com/navidrome/navidrome/core/transcode"
 )
 
 var Set = wire.NewSet(
@@ -20,6 +21,7 @@ var Set = wire.NewSet(
 	NewLibrary,
 	NewUser,
 	NewMaintenance,
+	transcode.NewDecider,
 	agents.GetAgents,
 	external.NewProvider,
 	wire.Bind(new(external.Agents), new(*agents.Agents)),

db/migrations/20260205120000_add_codec_and_update_transcodings.go

@@ -0,0 +1,63 @@
+package migrations
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/navidrome/navidrome/model/id"
+	"github.com/pressly/goose/v3"
+)
+
+func init() {
+	goose.AddMigrationContext(upAddCodecAndUpdateTranscodings, downAddCodecAndUpdateTranscodings)
+}
+
+func upAddCodecAndUpdateTranscodings(_ context.Context, tx *sql.Tx) error {
+	// Add codec column to media_file.
+	_, err := tx.Exec(`ALTER TABLE media_file ADD COLUMN codec VARCHAR(255) DEFAULT '' NOT NULL`)
+	if err != nil {
+		return err
+	}
+	_, err = tx.Exec(`CREATE INDEX IF NOT EXISTS media_file_codec ON media_file(codec)`)
+	if err != nil {
+		return err
+	}
+
+	// Update old AAC default (adts) to new default (ipod with fragmented MP4).
+	// Only affects users who still have the unmodified old default command.
+	_, err = tx.Exec(
+		`UPDATE transcoding SET command = ? WHERE target_format = 'aac' AND command = ?`,
+		"ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a aac -f ipod -movflags frag_keyframe+empty_moov -",
+		"ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a aac -f adts -",
+	)
+	if err != nil {
+		return err
+	}
+
+	// Add FLAC transcoding for existing installations that were seeded before FLAC was added.
+	var count int
+	err = tx.QueryRow("SELECT COUNT(*) FROM transcoding WHERE target_format = 'flac'").Scan(&count)
+	if err != nil {
+		return err
+	}
+	if count == 0 {
+		_, err = tx.Exec(
+			"INSERT INTO transcoding (id, name, target_format, default_bit_rate, command) VALUES (?, ?, ?, ?, ?)",
+			id.NewRandom(), "flac audio", "flac", 0,
+			"ffmpeg -i %s -ss %t -map 0:a:0 -v 0 -c:a flac -f flac -",
+		)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func downAddCodecAndUpdateTranscodings(_ context.Context, tx *sql.Tx) error {
+	_, err := tx.Exec(`DROP INDEX IF EXISTS media_file_codec`)
+	if err != nil {
+		return err
+	}
+	_, err = tx.Exec(`ALTER TABLE media_file DROP COLUMN codec`)
+	return err
+}

model/mediafile.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/gohugoio/hashstructure"
 	"github.com/navidrome/navidrome/conf"
+	confmime "github.com/navidrome/navidrome/conf/mime"
 	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/utils"
 	"github.com/navidrome/navidrome/utils/slice"
@@ -56,6 +57,7 @@ type MediaFile struct {
 	SampleRate           int      `structs:"sample_rate" json:"sampleRate"`
 	BitDepth             int      `structs:"bit_depth" json:"bitDepth"`
 	Channels             int      `structs:"channels" json:"channels"`
+	Codec                string   `structs:"codec" json:"codec"`
 	Genre                string   `structs:"genre" json:"genre"`
 	Genres               Genres   `structs:"-" json:"genres,omitempty"`
 	SortTitle            string   `structs:"sort_title" json:"sortTitle,omitempty"`
@@ -161,6 +163,81 @@ func (mf MediaFile) AbsolutePath() string {
 	return filepath.Join(mf.LibraryPath, mf.Path)
 }
 
+// AudioCodec returns the audio codec for this file.
+// Uses the stored Codec field if available, otherwise infers from Suffix and audio properties.
+func (mf MediaFile) AudioCodec() string {
+	// If we have a stored codec from scanning, normalize and return it
+	if mf.Codec != "" {
+		return strings.ToLower(mf.Codec)
+	}
+	// Fallback: infer from Suffix + BitDepth
+	return mf.inferCodecFromSuffix()
+}
+
+// inferCodecFromSuffix infers the codec from the file extension when Codec field is empty.
+func (mf MediaFile) inferCodecFromSuffix() string {
+	switch strings.ToLower(mf.Suffix) {
+	case "mp3", "mpga":
+		return "mp3"
+	case "mp2":
+		return "mp2"
+	case "ogg", "oga":
+		return "vorbis"
+	case "opus":
+		return "opus"
+	case "mpc":
+		return "mpc"
+	case "wma":
+		return "wma"
+	case "flac":
+		return "flac"
+	case "wav":
+		return "pcm"
+	case "aif", "aiff", "aifc":
+		return "pcm"
+	case "ape":
+		return "ape"
+	case "wv", "wvp":
+		return "wv"
+	case "tta":
+		return "tta"
+	case "tak":
+		return "tak"
+	case "shn":
+		return "shn"
+	case "dsf", "dff":
+		return "dsd"
+	case "m4a":
+		// AAC if BitDepth==0, ALAC if BitDepth>0
+		if mf.BitDepth > 0 {
+			return "alac"
+		}
+		return "aac"
+	case "m4b", "m4p", "m4r":
+		return "aac"
+	default:
+		return ""
+	}
+}
+
+// IsLossless returns true if this file uses a lossless codec.
+func (mf MediaFile) IsLossless() bool {
+	codec := mf.AudioCodec()
+	// Primary: codec-based check (most accurate for containers like M4A)
+	switch codec {
+	case "flac", "alac", "pcm", "ape", "wv", "tta", "tak", "shn", "dsd":
+		return true
+	}
+	// Secondary: suffix-based check using configurable list from YAML
+	if slices.Contains(confmime.LosslessFormats, mf.Suffix) {
+		return true
+	}
+	// Fallback heuristic: if BitDepth is set, it's likely lossless.
+	// This may produce false positives for lossy formats that report bit depth,
+	// but it becomes irrelevant once the Codec column is populated after a full rescan.
+	return mf.BitDepth > 0
+}
+
 type MediaFiles []MediaFile
 
 // ToAlbum creates an Album object based on the attributes of this MediaFiles collection.

model/mediafile_test.go

@@ -475,7 +475,7 @@ var _ = Describe("MediaFile", func() {
 		DeferCleanup(configtest.SetupConfig())
 		conf.Server.EnableMediaFileCoverArt = true
 	})
-	Describe(".CoverArtId()", func() {
+	Describe("CoverArtId", func() {
 		It("returns its own id if it HasCoverArt", func() {
 			mf := MediaFile{ID: "111", AlbumID: "1", HasCoverArt: true}
 			id := mf.CoverArtID()
@@ -496,6 +496,94 @@ var _ = Describe("MediaFile", func() {
 			Expect(id.ID).To(Equal(mf.AlbumID))
 		})
 	})
+
+	Describe("AudioCodec", func() {
+		It("returns normalized stored codec when available", func() {
+			mf := MediaFile{Codec: "AAC", Suffix: "m4a"}
+			Expect(mf.AudioCodec()).To(Equal("aac"))
+		})
+
+		It("returns stored codec lowercased", func() {
+			mf := MediaFile{Codec: "ALAC", Suffix: "m4a"}
+			Expect(mf.AudioCodec()).To(Equal("alac"))
+		})
+
+		DescribeTable("infers codec from suffix when Codec field is empty",
+			func(suffix string, bitDepth int, expected string) {
+				mf := MediaFile{Suffix: suffix, BitDepth: bitDepth}
+				Expect(mf.AudioCodec()).To(Equal(expected))
+			},
+			Entry("mp3", "mp3", 0, "mp3"),
+			Entry("mpga", "mpga", 0, "mp3"),
+			Entry("mp2", "mp2", 0, "mp2"),
+			Entry("ogg", "ogg", 0, "vorbis"),
+			Entry("oga", "oga", 0, "vorbis"),
+			Entry("opus", "opus", 0, "opus"),
+			Entry("mpc", "mpc", 0, "mpc"),
+			Entry("wma", "wma", 0, "wma"),
+			Entry("flac", "flac", 0, "flac"),
+			Entry("wav", "wav", 0, "pcm"),
+			Entry("aif", "aif", 0, "pcm"),
+			Entry("aiff", "aiff", 0, "pcm"),
+			Entry("aifc", "aifc", 0, "pcm"),
+			Entry("ape", "ape", 0, "ape"),
+			Entry("wv", "wv", 0, "wv"),
+			Entry("wvp", "wvp", 0, "wv"),
+			Entry("tta", "tta", 0, "tta"),
+			Entry("tak", "tak", 0, "tak"),
+			Entry("shn", "shn", 0, "shn"),
+			Entry("dsf", "dsf", 0, "dsd"),
+			Entry("dff", "dff", 0, "dsd"),
+			Entry("m4a with BitDepth=0 (AAC)", "m4a", 0, "aac"),
+			Entry("m4a with BitDepth>0 (ALAC)", "m4a", 16, "alac"),
+			Entry("m4b", "m4b", 0, "aac"),
+			Entry("m4p", "m4p", 0, "aac"),
+			Entry("m4r", "m4r", 0, "aac"),
+			Entry("unknown suffix", "xyz", 0, ""),
+		)
+
+		It("prefers stored codec over suffix inference", func() {
+			mf := MediaFile{Codec: "ALAC", Suffix: "m4a", BitDepth: 0}
+			Expect(mf.AudioCodec()).To(Equal("alac"))
+		})
+	})
+
+	Describe("IsLossless", func() {
+		BeforeEach(func() {
+			DeferCleanup(configtest.SetupConfig())
+		})
+
+		DescribeTable("detects lossless codecs",
+			func(codec string, suffix string, bitDepth int, expected bool) {
+				mf := MediaFile{Codec: codec, Suffix: suffix, BitDepth: bitDepth}
+				Expect(mf.IsLossless()).To(Equal(expected))
+			},
+			Entry("flac", "FLAC", "flac", 16, true),
+			Entry("alac", "ALAC", "m4a", 24, true),
+			Entry("pcm via wav", "", "wav", 16, true),
+			Entry("pcm via aiff", "", "aiff", 24, true),
+			Entry("ape", "", "ape", 16, true),
+			Entry("wv", "", "wv", 0, true),
+			Entry("tta", "", "tta", 0, true),
+			Entry("tak", "", "tak", 0, true),
+			Entry("shn", "", "shn", 0, true),
+			Entry("dsd", "", "dsf", 0, true),
+			Entry("mp3 is lossy", "MP3", "mp3", 0, false),
+			Entry("aac is lossy", "AAC", "m4a", 0, false),
+			Entry("vorbis is lossy", "", "ogg", 0, false),
+			Entry("opus is lossy", "", "opus", 0, false),
+		)
+
+		It("detects lossless via BitDepth fallback when codec is unknown", func() {
+			mf := MediaFile{Suffix: "xyz", BitDepth: 24}
+			Expect(mf.IsLossless()).To(BeTrue())
+		})
+
+		It("returns false for unknown with no BitDepth", func() {
+			mf := MediaFile{Suffix: "xyz", BitDepth: 0}
+			Expect(mf.IsLossless()).To(BeFalse())
+		})
+	})
 })
 
 func t(v string) time.Time {

model/metadata/map_mediafile.go

@@ -65,6 +65,7 @@ func (md Metadata) ToMediaFile(libID int, folderID string) model.MediaFile {
 	mf.SampleRate = md.AudioProperties().SampleRate
 	mf.BitDepth = md.AudioProperties().BitDepth
 	mf.Channels = md.AudioProperties().Channels
+	mf.Codec = md.AudioProperties().Codec
 	mf.Path = md.FilePath()
 	mf.Suffix = md.Suffix()
 	mf.Size = md.Size()

model/metadata/metadata.go

@@ -35,6 +35,7 @@ type AudioProperties struct {
 	BitDepth   int
 	SampleRate int
 	Channels   int
+	Codec      string
 }
 
 type Date string

server/e2e/e2e_suite_test.go

@@ -23,6 +23,7 @@ import (
 	"github.com/navidrome/navidrome/core/playback"
 	"github.com/navidrome/navidrome/core/scrobbler"
 	"github.com/navidrome/navidrome/core/storage/storagetest"
+	"github.com/navidrome/navidrome/core/transcode"
 	"github.com/navidrome/navidrome/db"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
@@ -189,14 +190,33 @@ func (n noopArtwork) GetOrPlaceholder(_ context.Context, _ string, _ int, _ bool
 // noopStreamer implements core.MediaStreamer
 type noopStreamer struct{}
 
-func (n noopStreamer) NewStream(context.Context, string, string, int, int) (*core.Stream, error) {
+func (n noopStreamer) NewStream(context.Context, core.StreamRequest) (*core.Stream, error) {
 	return nil, model.ErrNotFound
 }
 
-func (n noopStreamer) DoStream(context.Context, *model.MediaFile, string, int, int) (*core.Stream, error) {
+func (n noopStreamer) DoStream(context.Context, *model.MediaFile, core.StreamRequest) (*core.Stream, error) {
 	return nil, model.ErrNotFound
 }
 
+// noopDecider implements transcode.Decider
+type noopDecider struct{}
+
+func (n noopDecider) MakeDecision(context.Context, *model.MediaFile, *transcode.ClientInfo) (*transcode.Decision, error) {
+	return nil, nil
+}
+
+func (n noopDecider) CreateTranscodeParams(*transcode.Decision) (string, error) {
+	return "", nil
+}
+
+func (n noopDecider) ParseTranscodeParams(string) (*transcode.Params, error) {
+	return nil, nil
+}
+
+func (n noopDecider) ValidateTranscodeParams(context.Context, string, string) (*transcode.Params, *model.MediaFile, error) {
+	return nil, nil, nil
+}
+
 // noopArchiver implements core.Archiver
 type noopArchiver struct{}
 
@@ -265,6 +285,7 @@ var (
 	_ core.Archiver         = noopArchiver{}
 	_ external.Provider     = noopProvider{}
 	_ scrobbler.PlayTracker = noopPlayTracker{}
+	_ transcode.Decider     = noopDecider{}
 )
 
 var _ = BeforeSuite(func() {
@@ -344,6 +365,7 @@ func setupTestDB() {
 		core.NewShare(ds),
 		playback.PlaybackServer(nil),
 		metrics.NewNoopInstance(),
+		noopDecider{},
 	)
 }
 

server/public/handle_streams.go

@@ -8,6 +8,7 @@ import (
 	"strconv"
 
 	"github.com/lestrrat-go/jwx/v2/jwt"
+	"github.com/navidrome/navidrome/core"
 	"github.com/navidrome/navidrome/core/auth"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/utils/req"
@@ -24,10 +25,13 @@ func (pub *Router) handleStream(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	stream, err := pub.streamer.NewStream(ctx, info.id, info.format, info.bitrate, 0)
+	stream, err := pub.streamer.NewStream(ctx, core.StreamRequest{
+		ID: info.id, Format: info.format, BitRate: info.bitrate,
+	})
 	if err != nil {
 		log.Error(ctx, "Error starting shared stream", err)
 		http.Error(w, "invalid request", http.StatusInternalServerError)
+		return
 	}
 
 	// Make sure the stream will be closed at the end, to avoid leakage

server/subsonic/album_lists_test.go

@@ -27,7 +27,7 @@ var _ = Describe("Album Lists", func() {
 		ds = &tests.MockDataStore{}
 		auth.Init(ds)
 		mockRepo = ds.Album(ctx).(*tests.MockAlbumRepo)
-		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 		w = httptest.NewRecorder()
 	})
 

server/subsonic/api.go

@@ -17,6 +17,7 @@ import (
 	"github.com/navidrome/navidrome/core/metrics"
 	"github.com/navidrome/navidrome/core/playback"
 	"github.com/navidrome/navidrome/core/scrobbler"
+	"github.com/navidrome/navidrome/core/transcode"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/server"
@@ -47,12 +48,13 @@ type Router struct {
 	share             core.Share
 	playback          playback.PlaybackServer
 	metrics           metrics.Metrics
+	transcodeDecision transcode.Decider
 }
 
 func New(ds model.DataStore, artwork artwork.Artwork, streamer core.MediaStreamer, archiver core.Archiver,
 	players core.Players, provider external.Provider, scanner model.Scanner, broker events.Broker,
 	playlists core.Playlists, scrobbler scrobbler.PlayTracker, share core.Share, playback playback.PlaybackServer,
-	metrics metrics.Metrics,
+	metrics metrics.Metrics, transcodeDecision transcode.Decider,
 ) *Router {
 	r := &Router{
 		ds:                ds,
@@ -68,6 +70,7 @@ func New(ds model.DataStore, artwork artwork.Artwork, streamer core.MediaStreame
 		share:             share,
 		playback:          playback,
 		metrics:           metrics,
+		transcodeDecision: transcodeDecision,
 	}
 	r.Handler = r.routes()
 	return r
@@ -172,6 +175,8 @@ func (api *Router) routes() http.Handler {
 			h(r, "getLyricsBySongId", api.GetLyricsBySongId)
 			hr(r, "stream", api.Stream)
 			hr(r, "download", api.Download)
+			hr(r, "getTranscodeDecision", api.GetTranscodeDecision)
+			hr(r, "getTranscodeStream", api.GetTranscodeStream)
 		})
 		r.Group(func(r chi.Router) {
 			// configure request throttling

server/subsonic/media_annotation_test.go

@@ -27,7 +27,7 @@ var _ = Describe("MediaAnnotationController", func() {
 		ds = &tests.MockDataStore{}
 		playTracker = &fakePlayTracker{}
 		eventBroker = &fakeEventBroker{}
-		router = New(ds, nil, nil, nil, nil, nil, nil, eventBroker, nil, playTracker, nil, nil, nil)
+		router = New(ds, nil, nil, nil, nil, nil, nil, eventBroker, nil, playTracker, nil, nil, nil, nil)
 	})
 
 	Describe("Scrobble", func() {

server/subsonic/media_retrieval_test.go

@@ -33,7 +33,7 @@ var _ = Describe("MediaRetrievalController", func() {
 			MockedMediaFile: mockRepo,
 		}
 		artwork = &fakeArtwork{data: "image data"}
-		router = New(ds, artwork, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+		router = New(ds, artwork, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 		w = httptest.NewRecorder()
 		DeferCleanup(configtest.SetupConfig())
 		conf.Server.LyricsPriority = "embedded,.lrc"

server/subsonic/opensubsonic.go

@@ -13,6 +13,7 @@ func (api *Router) GetOpenSubsonicExtensions(_ *http.Request) (*responses.Subson
 		{Name: "formPost", Versions: []int32{1}},
 		{Name: "songLyrics", Versions: []int32{1}},
 		{Name: "indexBasedQueue", Versions: []int32{1}},
+		{Name: "transcoding", Versions: []int32{1}},
 	}
 	return response, nil
 }

server/subsonic/opensubsonic_test.go

@@ -19,7 +19,7 @@ var _ = Describe("GetOpenSubsonicExtensions", func() {
 	)
 
 	BeforeEach(func() {
-		router = subsonic.New(nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+		router = subsonic.New(nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 		w = httptest.NewRecorder()
 		r = httptest.NewRequest("GET", "/getOpenSubsonicExtensions?f=json", nil)
 	})
@@ -35,11 +35,12 @@ var _ = Describe("GetOpenSubsonicExtensions", func() {
 		err := json.Unmarshal(w.Body.Bytes(), &response)
 		Expect(err).NotTo(HaveOccurred())
 		Expect(*response.Subsonic.OpenSubsonicExtensions).To(SatisfyAll(
-			HaveLen(4),
+			HaveLen(5),
 			ContainElement(responses.OpenSubsonicExtension{Name: "transcodeOffset", Versions: []int32{1}}),
 			ContainElement(responses.OpenSubsonicExtension{Name: "formPost", Versions: []int32{1}}),
 			ContainElement(responses.OpenSubsonicExtension{Name: "songLyrics", Versions: []int32{1}}),
 			ContainElement(responses.OpenSubsonicExtension{Name: "indexBasedQueue", Versions: []int32{1}}),
+			ContainElement(responses.OpenSubsonicExtension{Name: "transcoding", Versions: []int32{1}}),
 		))
 	})
 })

server/subsonic/playlists_test.go

@@ -24,7 +24,7 @@ var _ = Describe("buildPlaylist", func() {
 
 	BeforeEach(func() {
 		ds = &tests.MockDataStore{}
-		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 		ctx = context.Background()
 	})
 
@@ -224,7 +224,7 @@ var _ = Describe("UpdatePlaylist", func() {
 	BeforeEach(func() {
 		ds = &tests.MockDataStore{}
 		playlists = &fakePlaylists{}
-		router = New(ds, nil, nil, nil, nil, nil, nil, nil, playlists, nil, nil, nil, nil)
+		router = New(ds, nil, nil, nil, nil, nil, nil, nil, playlists, nil, nil, nil, nil, nil)
 	})
 
 	It("clears the comment when parameter is empty", func() {

server/subsonic/responses/responses.go

@@ -61,6 +61,7 @@ type Subsonic struct {
 	OpenSubsonicExtensions *OpenSubsonicExtensions `xml:"openSubsonicExtensions,omitempty"  json:"openSubsonicExtensions,omitempty"`
 	LyricsList             *LyricsList             `xml:"lyricsList,omitempty"              json:"lyricsList,omitempty"`
 	PlayQueueByIndex       *PlayQueueByIndex       `xml:"playQueueByIndex,omitempty" json:"playQueueByIndex,omitempty"`
+	TranscodeDecision      *TranscodeDecision      `xml:"transcodeDecision,omitempty"       json:"transcodeDecision,omitempty"`
 }
 
 const (
@@ -617,3 +618,26 @@ func marshalJSONArray[T any](v []T) ([]byte, error) {
 	}
 	return json.Marshal(v)
 }
+
+// TranscodeDecision represents the response for getTranscodeDecision (OpenSubsonic transcoding extension)
+type TranscodeDecision struct {
+	CanDirectPlay    bool           `xml:"canDirectPlay,attr"               json:"canDirectPlay"`
+	CanTranscode     bool           `xml:"canTranscode,attr"                json:"canTranscode"`
+	TranscodeReasons []string       `xml:"transcodeReason,omitempty"        json:"transcodeReason,omitempty"`
+	ErrorReason      string         `xml:"errorReason,attr,omitempty"       json:"errorReason,omitempty"`
+	TranscodeParams  string         `xml:"transcodeParams,attr,omitempty"   json:"transcodeParams,omitempty"`
+	SourceStream     *StreamDetails `xml:"sourceStream,omitempty"           json:"sourceStream,omitempty"`
+	TranscodeStream  *StreamDetails `xml:"transcodeStream,omitempty"        json:"transcodeStream,omitempty"`
+}
+
+// StreamDetails describes audio stream properties for transcoding decisions
+type StreamDetails struct {
+	Protocol        string `xml:"protocol,attr,omitempty"        json:"protocol,omitempty"`
+	Container       string `xml:"container,attr,omitempty"       json:"container,omitempty"`
+	Codec           string `xml:"codec,attr,omitempty"           json:"codec,omitempty"`
+	AudioChannels   int32  `xml:"audioChannels,attr,omitempty"   json:"audioChannels,omitempty"`
+	AudioBitrate    int32  `xml:"audioBitrate,attr,omitempty"     json:"audioBitrate,omitempty"`
+	AudioProfile    string `xml:"audioProfile,attr,omitempty"    json:"audioProfile,omitempty"`
+	AudioSamplerate int32  `xml:"audioSamplerate,attr,omitempty" json:"audioSamplerate,omitempty"`
+	AudioBitdepth   int32  `xml:"audioBitdepth,attr,omitempty"   json:"audioBitdepth,omitempty"`
+}

server/subsonic/searching_test.go

@@ -21,7 +21,7 @@ var _ = Describe("Search", func() {
 		ds = &tests.MockDataStore{}
 		auth.Init(ds)
 
-		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
+		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil)
 
 		// Get references to the mock repositories so we can inspect their Options
 		mockAlbumRepo = ds.Album(nil).(*tests.MockAlbumRepo)

server/subsonic/stream.go

@@ -60,7 +60,9 @@ func (api *Router) Stream(w http.ResponseWriter, r *http.Request) (*responses.Su
 	format, _ := p.String("format")
 	timeOffset := p.IntOr("timeOffset", 0)
 
-	stream, err := api.streamer.NewStream(ctx, id, format, maxBitRate, timeOffset)
+	stream, err := api.streamer.NewStream(ctx, core.StreamRequest{
+		ID: id, Format: format, BitRate: maxBitRate, Offset: timeOffset,
+	})
 	if err != nil {
 		return nil, err
 	}
@@ -129,7 +131,9 @@ func (api *Router) Download(w http.ResponseWriter, r *http.Request) (*responses.
 
 	switch v := entity.(type) {
 	case *model.MediaFile:
-		stream, err := api.streamer.NewStream(ctx, id, format, maxBitRate, 0)
+		stream, err := api.streamer.NewStream(ctx, core.StreamRequest{
+			ID: id, Format: format, BitRate: maxBitRate,
+		})
 		if err != nil {
 			return nil, err
 		}

server/subsonic/transcode.go

@@ -0,0 +1,383 @@
+package subsonic
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"slices"
+	"strconv"
+
+	"github.com/navidrome/navidrome/core"
+	"github.com/navidrome/navidrome/core/transcode"
+	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/server/subsonic/responses"
+	"github.com/navidrome/navidrome/utils/req"
+)
+
+// API-layer request structs for JSON unmarshaling (decoupled from core structs)
+
+// clientInfoRequest represents client playback capabilities from the request body
+type clientInfoRequest struct {
+	Name                       string                      `json:"name,omitempty"`
+	Platform                   string                      `json:"platform,omitempty"`
+	MaxAudioBitrate            int                         `json:"maxAudioBitrate,omitempty"`
+	MaxTranscodingAudioBitrate int                         `json:"maxTranscodingAudioBitrate,omitempty"`
+	DirectPlayProfiles         []directPlayProfileRequest  `json:"directPlayProfiles,omitempty"`
+	TranscodingProfiles        []transcodingProfileRequest `json:"transcodingProfiles,omitempty"`
+	CodecProfiles              []codecProfileRequest       `json:"codecProfiles,omitempty"`
+}
+
+// directPlayProfileRequest describes a format the client can play directly
+type directPlayProfileRequest struct {
+	Containers       []string `json:"containers,omitempty"`
+	AudioCodecs      []string `json:"audioCodecs,omitempty"`
+	Protocols        []string `json:"protocols,omitempty"`
+	MaxAudioChannels int      `json:"maxAudioChannels,omitempty"`
+}
+
+// transcodingProfileRequest describes a transcoding target the client supports
+type transcodingProfileRequest struct {
+	Container        string `json:"container,omitempty"`
+	AudioCodec       string `json:"audioCodec,omitempty"`
+	Protocol         string `json:"protocol,omitempty"`
+	MaxAudioChannels int    `json:"maxAudioChannels,omitempty"`
+}
+
+// codecProfileRequest describes codec-specific limitations
+type codecProfileRequest struct {
+	Type        string              `json:"type,omitempty"`
+	Name        string              `json:"name,omitempty"`
+	Limitations []limitationRequest `json:"limitations,omitempty"`
+}
+
+// limitationRequest describes a specific codec limitation
+type limitationRequest struct {
+	Name       string   `json:"name,omitempty"`
+	Comparison string   `json:"comparison,omitempty"`
+	Values     []string `json:"values,omitempty"`
+	Required   bool     `json:"required,omitempty"`
+}
+
+// toCoreClientInfo converts the API request struct to the transcode.ClientInfo struct.
+// The OpenSubsonic spec uses bps for bitrate values; core uses kbps.
+func (r *clientInfoRequest) toCoreClientInfo() *transcode.ClientInfo {
+	ci := &transcode.ClientInfo{
+		Name:                       r.Name,
+		Platform:                   r.Platform,
+		MaxAudioBitrate:            bpsToKbps(r.MaxAudioBitrate),
+		MaxTranscodingAudioBitrate: bpsToKbps(r.MaxTranscodingAudioBitrate),
+	}
+
+	for _, dp := range r.DirectPlayProfiles {
+		ci.DirectPlayProfiles = append(ci.DirectPlayProfiles, transcode.DirectPlayProfile{
+			Containers:       dp.Containers,
+			AudioCodecs:      dp.AudioCodecs,
+			Protocols:        dp.Protocols,
+			MaxAudioChannels: dp.MaxAudioChannels,
+		})
+	}
+
+	for _, tp := range r.TranscodingProfiles {
+		ci.TranscodingProfiles = append(ci.TranscodingProfiles, transcode.Profile{
+			Container:        tp.Container,
+			AudioCodec:       tp.AudioCodec,
+			Protocol:         tp.Protocol,
+			MaxAudioChannels: tp.MaxAudioChannels,
+		})
+	}
+
+	for _, cp := range r.CodecProfiles {
+		coreCP := transcode.CodecProfile{
+			Type: cp.Type,
+			Name: cp.Name,
+		}
+		for _, lim := range cp.Limitations {
+			coreLim := transcode.Limitation{
+				Name:       lim.Name,
+				Comparison: lim.Comparison,
+				Values:     lim.Values,
+				Required:   lim.Required,
+			}
+			// Convert audioBitrate limitation values from bps to kbps
+			if lim.Name == transcode.LimitationAudioBitrate {
+				coreLim.Values = convertBitrateValues(lim.Values)
+			}
+			coreCP.Limitations = append(coreCP.Limitations, coreLim)
+		}
+		ci.CodecProfiles = append(ci.CodecProfiles, coreCP)
+	}
+
+	return ci
+}
+
+// bpsToKbps converts bits per second to kilobits per second (rounded).
+func bpsToKbps(bps int) int {
+	return (bps + 500) / 1000
+}
+
+// kbpsToBps converts kilobits per second to bits per second.
+func kbpsToBps(kbps int) int {
+	return kbps * 1000
+}
+
+// convertBitrateValues converts a slice of bps string values to kbps string values.
+func convertBitrateValues(bpsValues []string) []string {
+	result := make([]string, len(bpsValues))
+	for i, v := range bpsValues {
+		n, err := strconv.Atoi(v)
+		if err == nil {
+			result[i] = strconv.Itoa(bpsToKbps(n))
+		} else {
+			result[i] = v // preserve unparseable values as-is
+		}
+	}
+	return result
+}
+
+// validate checks that all enum fields in the request contain valid values per the OpenSubsonic spec.
+func (r *clientInfoRequest) validate() error {
+	for _, dp := range r.DirectPlayProfiles {
+		for _, p := range dp.Protocols {
+			if !isValidProtocol(p) {
+				return fmt.Errorf("invalid protocol: %s", p)
+			}
+		}
+	}
+	for _, tp := range r.TranscodingProfiles {
+		if tp.Protocol != "" && !isValidProtocol(tp.Protocol) {
+			return fmt.Errorf("invalid protocol: %s", tp.Protocol)
+		}
+	}
+	for _, cp := range r.CodecProfiles {
+		if !isValidCodecProfileType(cp.Type) {
+			return fmt.Errorf("invalid codec profile type: %s", cp.Type)
+		}
+		for _, lim := range cp.Limitations {
+			if !isValidLimitationName(lim.Name) {
+				return fmt.Errorf("invalid limitation name: %s", lim.Name)
+			}
+			if !isValidComparison(lim.Comparison) {
+				return fmt.Errorf("invalid comparison: %s", lim.Comparison)
+			}
+		}
+	}
+	return nil
+}
+
+var validProtocols = []string{
+	transcode.ProtocolHTTP,
+	transcode.ProtocolHLS,
+}
+
+func isValidProtocol(p string) bool {
+	return slices.Contains(validProtocols, p)
+}
+
+var validCodecProfileTypes = []string{
+	transcode.CodecProfileTypeAudio,
+}
+
+func isValidCodecProfileType(t string) bool {
+	return slices.Contains(validCodecProfileTypes, t)
+}
+
+var validLimitationNames = []string{
+	transcode.LimitationAudioChannels,
+	transcode.LimitationAudioBitrate,
+	transcode.LimitationAudioProfile,
+	transcode.LimitationAudioSamplerate,
+	transcode.LimitationAudioBitdepth,
+}
+
+func isValidLimitationName(n string) bool {
+	return slices.Contains(validLimitationNames, n)
+}
+
+var validComparisons = []string{
+	transcode.ComparisonEquals,
+	transcode.ComparisonNotEquals,
+	transcode.ComparisonLessThanEqual,
+	transcode.ComparisonGreaterThanEqual,
+}
+
+func isValidComparison(c string) bool {
+	return slices.Contains(validComparisons, c)
+}
+
+// GetTranscodeDecision handles the OpenSubsonic getTranscodeDecision endpoint.
+// It receives client capabilities and returns a decision on whether to direct play or transcode.
+func (api *Router) GetTranscodeDecision(w http.ResponseWriter, r *http.Request) (*responses.Subsonic, error) {
+	if r.Method != http.MethodPost {
+		w.Header().Set("Allow", "POST")
+		http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
+		return nil, nil
+	}
+
+	ctx := r.Context()
+	p := req.Params(r)
+
+	mediaID, err := p.String("mediaId")
+	if err != nil {
+		return nil, newError(responses.ErrorMissingParameter, "missing required parameter: mediaId")
+	}
+
+	mediaType, err := p.String("mediaType")
+	if err != nil {
+		return nil, newError(responses.ErrorMissingParameter, "missing required parameter: mediaType")
+	}
+
+	// Only support songs for now
+	if mediaType != "song" {
+		return nil, newError(responses.ErrorGeneric, "mediaType '%s' is not yet supported", mediaType)
+	}
+
+	// Parse and validate ClientInfo from request body (required per OpenSubsonic spec)
+	var clientInfoReq clientInfoRequest
+	r.Body = http.MaxBytesReader(w, r.Body, 1<<20) // 1 MB limit
+	if err := json.NewDecoder(r.Body).Decode(&clientInfoReq); err != nil {
+		return nil, newError(responses.ErrorGeneric, "invalid JSON request body")
+	}
+	if err := clientInfoReq.validate(); err != nil {
+		return nil, newError(responses.ErrorGeneric, "%v", err)
+	}
+	clientInfo := clientInfoReq.toCoreClientInfo()
+
+	// Get media file
+	mf, err := api.ds.MediaFile(ctx).Get(mediaID)
+	if err != nil {
+		if errors.Is(err, model.ErrNotFound) {
+			return nil, newError(responses.ErrorDataNotFound, "media file not found: %s", mediaID)
+		}
+		return nil, newError(responses.ErrorGeneric, "error retrieving media file: %v", err)
+	}
+
+	// Make the decision
+	decision, err := api.transcodeDecision.MakeDecision(ctx, mf, clientInfo)
+	if err != nil {
+		return nil, newError(responses.ErrorGeneric, "failed to make transcode decision: %v", err)
+	}
+
+	// Only create a token when there is a valid playback path
+	var transcodeParams string
+	if decision.CanDirectPlay || decision.CanTranscode {
+		transcodeParams, err = api.transcodeDecision.CreateTranscodeParams(decision)
+		if err != nil {
+			return nil, newError(responses.ErrorGeneric, "failed to create transcode token: %v", err)
+		}
+	}
+
+	// Build response (convert kbps from core to bps for the API)
+	response := newResponse()
+	response.TranscodeDecision = &responses.TranscodeDecision{
+		CanDirectPlay:    decision.CanDirectPlay,
+		CanTranscode:     decision.CanTranscode,
+		TranscodeReasons: decision.TranscodeReasons,
+		ErrorReason:      decision.ErrorReason,
+		TranscodeParams:  transcodeParams,
+		SourceStream: &responses.StreamDetails{
+			Protocol:        "http",
+			Container:       decision.SourceStream.Container,
+			Codec:           decision.SourceStream.Codec,
+			AudioBitrate:    int32(kbpsToBps(decision.SourceStream.Bitrate)),
+			AudioProfile:    decision.SourceStream.Profile,
+			AudioSamplerate: int32(decision.SourceStream.SampleRate),
+			AudioBitdepth:   int32(decision.SourceStream.BitDepth),
+			AudioChannels:   int32(decision.SourceStream.Channels),
+		},
+	}
+
+	if decision.TranscodeStream != nil {
+		response.TranscodeDecision.TranscodeStream = &responses.StreamDetails{
+			Protocol:        "http",
+			Container:       decision.TranscodeStream.Container,
+			Codec:           decision.TranscodeStream.Codec,
+			AudioBitrate:    int32(kbpsToBps(decision.TranscodeStream.Bitrate)),
+			AudioProfile:    decision.TranscodeStream.Profile,
+			AudioSamplerate: int32(decision.TranscodeStream.SampleRate),
+			AudioBitdepth:   int32(decision.TranscodeStream.BitDepth),
+			AudioChannels:   int32(decision.TranscodeStream.Channels),
+		}
+	}
+
+	return response, nil
+}
+
+// GetTranscodeStream handles the OpenSubsonic getTranscodeStream endpoint.
+// It streams media using the decision encoded in the transcodeParams JWT token.
+// All errors are returned as proper HTTP status codes (not Subsonic error responses).
+func (api *Router) GetTranscodeStream(w http.ResponseWriter, r *http.Request) (*responses.Subsonic, error) {
+	ctx := r.Context()
+	p := req.Params(r)
+
+	mediaID, err := p.String("mediaId")
+	if err != nil {
+		http.Error(w, "Bad Request", http.StatusBadRequest)
+		return nil, nil
+	}
+
+	mediaType, err := p.String("mediaType")
+	if err != nil {
+		http.Error(w, "Bad Request", http.StatusBadRequest)
+		return nil, nil
+	}
+
+	transcodeParamsToken, err := p.String("transcodeParams")
+	if err != nil {
+		http.Error(w, "Bad Request", http.StatusBadRequest)
+		return nil, nil
+	}
+
+	// Only support songs for now
+	if mediaType != "song" {
+		http.Error(w, "Bad Request", http.StatusBadRequest)
+		return nil, nil
+	}
+
+	// Validate the token, mediaID match, file existence, and freshness
+	params, mf, err := api.transcodeDecision.ValidateTranscodeParams(ctx, transcodeParamsToken, mediaID)
+	if err != nil {
+		switch {
+		case errors.Is(err, transcode.ErrMediaNotFound):
+			http.Error(w, "Not Found", http.StatusNotFound)
+		case errors.Is(err, transcode.ErrTokenInvalid), errors.Is(err, transcode.ErrTokenStale):
+			http.Error(w, "Gone", http.StatusGone)
+		default:
+			log.Error(ctx, "Error validating transcode params", err)
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		}
+		return nil, nil
+	}
+
+	// Build streaming parameters from the token
+	streamReq := core.StreamRequest{ID: mediaID, Offset: p.IntOr("offset", 0)}
+	if !params.DirectPlay && params.TargetFormat != "" {
+		streamReq.Format = params.TargetFormat
+		streamReq.BitRate = params.TargetBitrate // Already in kbps, matching the streamer
+		streamReq.SampleRate = params.TargetSampleRate
+		streamReq.BitDepth = params.TargetBitDepth
+		streamReq.Channels = params.TargetChannels
+	}
+
+	// Create stream (use DoStream to avoid duplicate DB fetch)
+	stream, err := api.streamer.DoStream(ctx, mf, streamReq)
+	if err != nil {
+		log.Error(ctx, "Error creating stream", "mediaID", mediaID, err)
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return nil, nil
+	}
+
+	// Make sure the stream will be closed at the end
+	defer func() {
+		if err := stream.Close(); err != nil && log.IsGreaterOrEqualTo(log.LevelDebug) {
+			log.Error("Error closing stream", "id", mediaID, "file", stream.Name(), err)
+		}
+	}()
+
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+
+	api.serveStream(ctx, w, r, stream, mediaID)
+
+	return nil, nil
+}

server/subsonic/transcode_test.go

@@ -0,0 +1,406 @@
+package subsonic
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+
+	"github.com/navidrome/navidrome/core"
+	"github.com/navidrome/navidrome/core/transcode"
+	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/tests"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Transcode endpoints", func() {
+	var (
+		router     *Router
+		ds         *tests.MockDataStore
+		mockTD     *mockTranscodeDecision
+		w          *httptest.ResponseRecorder
+		mockMFRepo *tests.MockMediaFileRepo
+	)
+
+	BeforeEach(func() {
+		mockMFRepo = &tests.MockMediaFileRepo{}
+		ds = &tests.MockDataStore{MockedMediaFile: mockMFRepo}
+		mockTD = &mockTranscodeDecision{}
+		router = New(ds, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, mockTD)
+		w = httptest.NewRecorder()
+	})
+
+	Describe("GetTranscodeDecision", func() {
+		It("returns 405 for non-POST requests", func() {
+			r := newGetRequest("mediaId=123", "mediaType=song")
+			resp, err := router.GetTranscodeDecision(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusMethodNotAllowed))
+			Expect(w.Header().Get("Allow")).To(Equal("POST"))
+		})
+
+		It("returns error when mediaId is missing", func() {
+			r := newJSONPostRequest("mediaType=song", "{}")
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("returns error when mediaType is missing", func() {
+			r := newJSONPostRequest("mediaId=123", "{}")
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("returns error for unsupported mediaType", func() {
+			r := newJSONPostRequest("mediaId=123&mediaType=podcast", "{}")
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("not yet supported"))
+		})
+
+		It("returns error when media file not found", func() {
+			mockMFRepo.SetError(true)
+			r := newJSONPostRequest("mediaId=notfound&mediaType=song", "{}")
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("returns error when body is empty", func() {
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", "")
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("returns error when body contains invalid JSON", func() {
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", "not-json{{{")
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+		})
+
+		It("returns error for invalid protocol in direct play profile", func() {
+			body := `{"directPlayProfiles":[{"containers":["mp3"],"audioCodecs":["mp3"],"protocols":["ftp"]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid protocol"))
+		})
+
+		It("returns error for invalid comparison operator", func() {
+			body := `{"codecProfiles":[{"type":"AudioCodec","name":"mp3","limitations":[{"name":"audioBitrate","comparison":"InvalidOp","values":["320"]}]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid comparison"))
+		})
+
+		It("returns error for invalid limitation name", func() {
+			body := `{"codecProfiles":[{"type":"AudioCodec","name":"mp3","limitations":[{"name":"unknownField","comparison":"Equals","values":["320"]}]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid limitation name"))
+		})
+
+		It("returns error for invalid codec profile type", func() {
+			body := `{"codecProfiles":[{"type":"VideoCodec","name":"mp3"}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid codec profile type"))
+		})
+
+		It("rejects wrong-case protocol", func() {
+			body := `{"directPlayProfiles":[{"containers":["mp3"],"audioCodecs":["mp3"],"protocols":["HTTP"]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid protocol"))
+		})
+
+		It("rejects wrong-case codec profile type", func() {
+			body := `{"codecProfiles":[{"type":"audiocodec","name":"mp3"}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid codec profile type"))
+		})
+
+		It("rejects wrong-case comparison operator", func() {
+			body := `{"codecProfiles":[{"type":"AudioCodec","name":"mp3","limitations":[{"name":"audioBitrate","comparison":"lessthanequal","values":["320"]}]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid comparison"))
+		})
+
+		It("rejects wrong-case limitation name", func() {
+			body := `{"codecProfiles":[{"type":"AudioCodec","name":"mp3","limitations":[{"name":"AudioBitrate","comparison":"Equals","values":["320"]}]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			_, err := router.GetTranscodeDecision(w, r)
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(ContainSubstring("invalid limitation name"))
+		})
+
+		It("returns a valid decision response", func() {
+			mockMFRepo.SetData(model.MediaFiles{
+				{ID: "song-1", Suffix: "mp3", Codec: "MP3", BitRate: 320, Channels: 2, SampleRate: 44100},
+			})
+			mockTD.decision = &transcode.Decision{
+				MediaID:       "song-1",
+				CanDirectPlay: true,
+				SourceStream: transcode.StreamDetails{
+					Container: "mp3", Codec: "mp3", Bitrate: 320,
+					SampleRate: 44100, Channels: 2,
+				},
+			}
+			mockTD.token = "test-jwt-token"
+
+			body := `{"directPlayProfiles":[{"containers":["mp3"],"protocols":["http"]}]}`
+			r := newJSONPostRequest("mediaId=song-1&mediaType=song", body)
+			resp, err := router.GetTranscodeDecision(w, r)
+
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp.TranscodeDecision).ToNot(BeNil())
+			Expect(resp.TranscodeDecision.CanDirectPlay).To(BeTrue())
+			Expect(resp.TranscodeDecision.TranscodeParams).To(Equal("test-jwt-token"))
+			Expect(resp.TranscodeDecision.SourceStream).ToNot(BeNil())
+			Expect(resp.TranscodeDecision.SourceStream.Protocol).To(Equal("http"))
+			Expect(resp.TranscodeDecision.SourceStream.Container).To(Equal("mp3"))
+			Expect(resp.TranscodeDecision.SourceStream.AudioBitrate).To(Equal(int32(320_000)))
+		})
+
+		It("includes transcode stream when transcoding", func() {
+			mockMFRepo.SetData(model.MediaFiles{
+				{ID: "song-2", Suffix: "flac", Codec: "FLAC", BitRate: 1000, Channels: 2, SampleRate: 96000, BitDepth: 24},
+			})
+			mockTD.decision = &transcode.Decision{
+				MediaID:          "song-2",
+				CanDirectPlay:    false,
+				CanTranscode:     true,
+				TargetFormat:     "mp3",
+				TargetBitrate:    256,
+				TranscodeReasons: []string{"container not supported"},
+				SourceStream: transcode.StreamDetails{
+					Container: "flac", Codec: "flac", Bitrate: 1000,
+					SampleRate: 96000, BitDepth: 24, Channels: 2,
+				},
+				TranscodeStream: &transcode.StreamDetails{
+					Container: "mp3", Codec: "mp3", Bitrate: 256,
+					SampleRate: 96000, Channels: 2,
+				},
+			}
+			mockTD.token = "transcode-token"
+
+			r := newJSONPostRequest("mediaId=song-2&mediaType=song", "{}")
+			resp, err := router.GetTranscodeDecision(w, r)
+
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp.TranscodeDecision.CanTranscode).To(BeTrue())
+			Expect(resp.TranscodeDecision.TranscodeReasons).To(ConsistOf("container not supported"))
+			Expect(resp.TranscodeDecision.TranscodeStream).ToNot(BeNil())
+			Expect(resp.TranscodeDecision.TranscodeStream.Container).To(Equal("mp3"))
+		})
+	})
+
+	Describe("GetTranscodeStream", func() {
+		It("returns 400 when mediaId is missing", func() {
+			r := newGetRequest("mediaType=song", "transcodeParams=abc")
+			resp, err := router.GetTranscodeStream(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusBadRequest))
+		})
+
+		It("returns 400 when transcodeParams is missing", func() {
+			r := newGetRequest("mediaId=123", "mediaType=song")
+			resp, err := router.GetTranscodeStream(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusBadRequest))
+		})
+
+		It("returns 410 for invalid token", func() {
+			mockTD.validateErr = transcode.ErrTokenInvalid
+			r := newGetRequest("mediaId=123", "mediaType=song", "transcodeParams=bad-token")
+			resp, err := router.GetTranscodeStream(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusGone))
+		})
+
+		It("returns 410 when mediaId doesn't match token", func() {
+			mockTD.validateErr = transcode.ErrTokenInvalid
+			r := newGetRequest("mediaId=wrong-id", "mediaType=song", "transcodeParams=valid-token")
+			resp, err := router.GetTranscodeStream(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusGone))
+		})
+
+		It("returns 404 when media file not found", func() {
+			mockTD.validateErr = transcode.ErrMediaNotFound
+			r := newGetRequest("mediaId=gone-id", "mediaType=song", "transcodeParams=valid-token")
+			resp, err := router.GetTranscodeStream(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusNotFound))
+		})
+
+		It("returns 410 when media file has changed (stale token)", func() {
+			mockTD.validateErr = transcode.ErrTokenStale
+			r := newGetRequest("mediaId=song-1", "mediaType=song", "transcodeParams=stale-token")
+			resp, err := router.GetTranscodeStream(w, r)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(resp).To(BeNil())
+			Expect(w.Code).To(Equal(http.StatusGone))
+		})
+
+		It("builds correct StreamRequest for direct play", func() {
+			fakeStreamer := &fakeMediaStreamer{}
+			router = New(ds, nil, fakeStreamer, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, mockTD)
+			mockTD.validateParams = &transcode.Params{MediaID: "song-1", DirectPlay: true}
+			mockTD.validateMF = &model.MediaFile{ID: "song-1"}
+
+			r := newGetRequest("mediaId=song-1", "mediaType=song", "transcodeParams=valid-token")
+			_, _ = router.GetTranscodeStream(w, r)
+
+			Expect(fakeStreamer.captured).ToNot(BeNil())
+			Expect(fakeStreamer.captured.ID).To(Equal("song-1"))
+			Expect(fakeStreamer.captured.Format).To(BeEmpty())
+			Expect(fakeStreamer.captured.BitRate).To(BeZero())
+			Expect(fakeStreamer.captured.SampleRate).To(BeZero())
+			Expect(fakeStreamer.captured.BitDepth).To(BeZero())
+			Expect(fakeStreamer.captured.Channels).To(BeZero())
+		})
+
+		It("builds correct StreamRequest for transcoding", func() {
+			fakeStreamer := &fakeMediaStreamer{}
+			router = New(ds, nil, fakeStreamer, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, mockTD)
+			mockTD.validateParams = &transcode.Params{
+				MediaID:          "song-2",
+				DirectPlay:       false,
+				TargetFormat:     "mp3",
+				TargetBitrate:    256,
+				TargetSampleRate: 44100,
+				TargetBitDepth:   16,
+				TargetChannels:   2,
+			}
+			mockTD.validateMF = &model.MediaFile{ID: "song-2"}
+
+			r := newGetRequest("mediaId=song-2", "mediaType=song", "transcodeParams=valid-token", "offset=10")
+			_, _ = router.GetTranscodeStream(w, r)
+
+			Expect(fakeStreamer.captured).ToNot(BeNil())
+			Expect(fakeStreamer.captured.ID).To(Equal("song-2"))
+			Expect(fakeStreamer.captured.Format).To(Equal("mp3"))
+			Expect(fakeStreamer.captured.BitRate).To(Equal(256))
+			Expect(fakeStreamer.captured.SampleRate).To(Equal(44100))
+			Expect(fakeStreamer.captured.BitDepth).To(Equal(16))
+			Expect(fakeStreamer.captured.Channels).To(Equal(2))
+			Expect(fakeStreamer.captured.Offset).To(Equal(10))
+		})
+	})
+
+	Describe("bpsToKbps", func() {
+		It("converts standard bitrates", func() {
+			Expect(bpsToKbps(128000)).To(Equal(128))
+			Expect(bpsToKbps(320000)).To(Equal(320))
+			Expect(bpsToKbps(256000)).To(Equal(256))
+		})
+		It("returns 0 for 0", func() {
+			Expect(bpsToKbps(0)).To(Equal(0))
+		})
+		It("rounds instead of truncating", func() {
+			Expect(bpsToKbps(999)).To(Equal(1))
+			Expect(bpsToKbps(500)).To(Equal(1))
+			Expect(bpsToKbps(499)).To(Equal(0))
+		})
+	})
+
+	Describe("kbpsToBps", func() {
+		It("converts standard bitrates", func() {
+			Expect(kbpsToBps(128)).To(Equal(128000))
+			Expect(kbpsToBps(320)).To(Equal(320000))
+		})
+		It("returns 0 for 0", func() {
+			Expect(kbpsToBps(0)).To(Equal(0))
+		})
+	})
+
+	Describe("convertBitrateValues", func() {
+		It("converts valid bps strings to kbps", func() {
+			Expect(convertBitrateValues([]string{"128000", "320000"})).To(Equal([]string{"128", "320"}))
+		})
+		It("preserves unparseable values", func() {
+			Expect(convertBitrateValues([]string{"128000", "bad", "320000"})).To(Equal([]string{"128", "bad", "320"}))
+		})
+		It("handles empty slice", func() {
+			Expect(convertBitrateValues([]string{})).To(Equal([]string{}))
+		})
+	})
+})
+
+// newJSONPostRequest creates an HTTP POST request with JSON body and query params
+func newJSONPostRequest(queryParams string, jsonBody string) *http.Request {
+	r := httptest.NewRequest("POST", "/getTranscodeDecision?"+queryParams, bytes.NewBufferString(jsonBody))
+	r.Header.Set("Content-Type", "application/json")
+	return r
+}
+
+// mockTranscodeDecision is a test double for transcode.Decider
+type mockTranscodeDecision struct {
+	decision       *transcode.Decision
+	token          string
+	tokenErr       error
+	params         *transcode.Params
+	parseErr       error
+	validateParams *transcode.Params
+	validateMF     *model.MediaFile
+	validateErr    error
+}
+
+func (m *mockTranscodeDecision) MakeDecision(_ context.Context, _ *model.MediaFile, _ *transcode.ClientInfo) (*transcode.Decision, error) {
+	if m.decision != nil {
+		return m.decision, nil
+	}
+	return &transcode.Decision{}, nil
+}
+
+func (m *mockTranscodeDecision) CreateTranscodeParams(_ *transcode.Decision) (string, error) {
+	return m.token, m.tokenErr
+}
+
+func (m *mockTranscodeDecision) ParseTranscodeParams(_ string) (*transcode.Params, error) {
+	if m.parseErr != nil {
+		return nil, m.parseErr
+	}
+	return m.params, nil
+}
+
+func (m *mockTranscodeDecision) ValidateTranscodeParams(_ context.Context, _ string, _ string) (*transcode.Params, *model.MediaFile, error) {
+	if m.validateErr != nil {
+		return nil, nil, m.validateErr
+	}
+	return m.validateParams, m.validateMF, nil
+}
+
+// fakeMediaStreamer captures the StreamRequest and returns a sentinel error,
+// allowing tests to verify parameter passing without constructing a real Stream.
+var errStreamCaptured = errors.New("stream request captured")
+
+type fakeMediaStreamer struct {
+	captured *core.StreamRequest
+}
+
+func (f *fakeMediaStreamer) NewStream(_ context.Context, req core.StreamRequest) (*core.Stream, error) {
+	f.captured = &req
+	return nil, errStreamCaptured
+}
+
+func (f *fakeMediaStreamer) DoStream(_ context.Context, _ *model.MediaFile, req core.StreamRequest) (*core.Stream, error) {
+	f.captured = &req
+	return nil, errStreamCaptured
+}

tests/mock_ffmpeg.go

@@ -6,6 +6,8 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
+
+	"github.com/navidrome/navidrome/core/ffmpeg"
 )
 
 func NewMockFFmpeg(data string) *MockFFmpeg {
@@ -23,7 +25,7 @@ func (ff *MockFFmpeg) IsAvailable() bool {
 	return true
 }
 
-func (ff *MockFFmpeg) Transcode(context.Context, string, string, int, int) (io.ReadCloser, error) {
+func (ff *MockFFmpeg) Transcode(_ context.Context, _ ffmpeg.TranscodeOptions) (io.ReadCloser, error) {
 	if ff.Error != nil {
 		return nil, ff.Error
 	}

tests/mock_transcoding_repo.go

@@ -18,6 +18,10 @@ func (m *MockTranscodingRepo) FindByFormat(format string) (*model.Transcoding, e
 		return &model.Transcoding{ID: "oga1", TargetFormat: "oga", DefaultBitRate: 128}, nil
 	case "opus":
 		return &model.Transcoding{ID: "opus1", TargetFormat: "opus", DefaultBitRate: 96}, nil
+	case "flac":
+		return &model.Transcoding{ID: "flac1", TargetFormat: "flac", DefaultBitRate: 0, Command: "ffmpeg -i %s -ss %t -map 0:a:0 -v 0 -c:a flac -f flac -"}, nil
+	case "aac":
+		return &model.Transcoding{ID: "aac1", TargetFormat: "aac", DefaultBitRate: 256, Command: "ffmpeg -i %s -ss %t -map 0:a:0 -b:a %bk -v 0 -c:a aac -f ipod -movflags frag_keyframe+empty_moov -"}, nil
 	default:
 		return nil, model.ErrNotFound
 	}