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8dee15501f
The FLAC and mp3 repairs had grown into two copies of the same wrapper: the same lazy peek on the first Read, the same MultiReader hand-off, the same tolerance of a short read, and the same comment twice. They now share one headerPatcher, with a prefix function per container. Transcode no longer selects the patcher by opts.Format. That string is the target format of a transcoding profile, which users can name anything, so a row called 'mp3 320' running the default mp3 command got no repair at all, while a row whose command emits FLAC got one only because the FLAC arm was the default. The shared peek dispatches on the magic bytes instead, which both patchers already had to check, and leaves anything it does not recognize untouched. Also drops b2i in favour of gg.If, and lowers the ID3 bound to 64KB: ffmpeg cannot write an attached picture to a non-seekable output, so the tag ffmpeg pipes out stays small.
41 lines
1.2 KiB
Go
41 lines
1.2 KiB
Go
package ffmpeg
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import (
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"encoding/binary"
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"math"
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)
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const (
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flacPrefixLen = 26 // through the last total_samples byte
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flacMaxTotalSamples = 1<<36 - 1
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)
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// flacPrefix fills in the STREAMINFO total_samples that ffmpeg leaves at 0 when
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// writing to a pipe, since a decoder cannot seek a cached FLAC without it.
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func (h *headerPatcher) flacPrefix(buf []byte) ([]byte, error) {
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buf, err := h.fill(buf, flacPrefixLen)
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if err != nil || len(buf) < flacPrefixLen {
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return buf, err
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}
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setFLACTotalSamples(buf, h.duration)
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return buf, nil
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}
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// setFLACTotalSamples takes the rate from the header rather than the transcode
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// options, so a resampled (-ar) output still gets the right count.
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func setFLACTotalSamples(prefix []byte, duration float32) {
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if prefix[4]&0x7F != 0 { // the first metadata block must be STREAMINFO
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return
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}
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// 20-bit rate | 3-bit channels | 5-bit depth | 36-bit total_samples
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info := binary.BigEndian.Uint64(prefix[18:])
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rate := info >> 44
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if rate == 0 || info&flacMaxTotalSamples != 0 {
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return
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}
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total := math.Round(float64(duration) * float64(rate))
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if total > flacMaxTotalSamples {
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return
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}
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binary.BigEndian.PutUint64(prefix[18:], info|uint64(total))
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}
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