navidrome/core/stream/codec.go

package stream

import "strings"

// normalizeProbeCodec maps ffprobe codec_name values to the simplified internal
// codec names used throughout Navidrome (matching inferCodecFromSuffix output).
// Most ffprobe names match directly; this handles the exceptions.
func normalizeProbeCodec(codec string) string {
	c := strings.ToLower(codec)
	// DSD variants: dsd_lsbf_planar, dsd_msbf_planar, dsd_lsbf, dsd_msbf
	if strings.HasPrefix(c, "dsd") {
		return "dsd"
	}
	// PCM variants: pcm_s16le, pcm_s24le, pcm_s32be, pcm_f32le, etc.
	if strings.HasPrefix(c, "pcm_") {
		return "pcm"
	}
	return c
}

// isLosslessFormat returns true if the format is a known lossless audio codec/format.
// Detection is based on codec name only, not bit depth — some lossy codecs (e.g. ADPCM)
// report non-zero bits_per_sample in ffprobe, so bit depth alone is not a reliable signal.
//
// Note: core/ffmpeg has a separate isLosslessOutputFormat that covers only formats
// ffmpeg can produce as output (a smaller set).
func isLosslessFormat(format string) bool {
	switch strings.ToLower(format) {
	case "flac", "alac", "wav", "aiff", "ape", "wv", "wavpack", "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
}