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Deluan
89026012ab
The FLAC muxer writes STREAMINFO before it knows the stream length, then rewinds at the end to fill total_samples in. Navidrome pipes ffmpeg's stdout (-f flac -), which is not seekable, so ffmpeg logs "unable to rewrite FLAC header" and the field stays 0. A decoder needs total_samples to turn a timestamp into a byte offset, so it reports an unknown duration and refuses to seek. Online playback hides this because the client re-requests with a new offset each time, but an offline copy is permanently unseekable, the symptom reported against Symfonium where seeking a downloaded track jumps back to the start. Transcode now wraps its own output and rewrites total_samples as the first bytes flow past. This lives in core/ffmpeg because the unseekable pipe is that package's doing: buildDynamicArgs is what appends the trailing '-'. core/stream only learns a target format and hands back an io.ReadCloser, so compensating there leaked a transcoder implementation detail one layer up. TranscodeOptions grows a Duration field alongside the existing Offset, which also puts the duration-minus-offset arithmetic in the same function that emits -ss. The wrapper runs on every transcode rather than only FLAC targets: the format on a transcoding row is a declared target that nothing validates against the command's actual -f, so a custom command can emit FLAC under any target_format. The magic-byte check inside the wrapper is the authoritative test and costs a 26-byte peek. The output sample rate is read back out of the header ffmpeg just wrote rather than taken from the transcode options, so a resampled (-ar) output still gets the right count. Anything that is not a FLAC stream with an unset total_samples passes through byte for byte. Measured on a 177s source: before, total_samples=0 and ffprobe reported duration N/A; after, total_samples=7807023 and duration 177.03s, with the audio payload byte-identical. This affects every piped FLAC regardless of the source format; only FLAC stores an authoritative "unknown", which is why mp3, opus and aac survive the same pipe. No SEEKTABLE is synthesised and the MD5 is left zero: both are optional, and decoders binary-search using total_samples alone.