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av_common: trim FLAC extradata when copying codec params

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For muxing, FFmpeg expects the FLAC extradata to be just the bare STREAMINFO,
and passing the full FLAC extradata (fLaC header and block size, with any
additional channel layout metadata) will result in malformed output, as
ffmpeg will simply prefix another fLaC header in front.
This can be considered to be a bug.

FFmpeg's own demuxers only store the STREAMINFO, hence the naivety, while
our common source of FLAC streams, the matroska demuxer, holds onto the
full extradata. It has been deemed preferable to adjust the extradata upon
muxing, instead of in the demuxer (ffmpeg's FLAC decoder knows to read
the full fLaC extradata).

This fixes muxing FLAC streams, meaning recorder.c or dump-cache.
This commit is contained in:
TheAMM 2021-07-06 00:30:18 +03:00 committed by Jan Ekström
parent dd9ed47c99
commit b0386fc543
1 changed files with 15 additions and 4 deletions
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19
common/av_common.c
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@ -80,12 +80,23 @@ AVCodecParameters *mp_codec_params_to_av(struct mp_codec_params *c)
avp->codec_id = mp_codec_to_av_codec_id(c->codec);
avp->codec_tag = c->codec_tag;
if (c->extradata_size) {
avp->extradata =
av_mallocz(c->extradata_size + AV_INPUT_BUFFER_PADDING_SIZE);
uint8_t *extradata = c->extradata;
int size = c->extradata_size;
if (avp->codec_id == AV_CODEC_ID_FLAC) {
// ffmpeg expects FLAC extradata to be just the STREAMINFO,
// so grab only that (and assume it'll be the first block)
if (size >= 8 && !memcmp(c->extradata, "fLaC", 4)) {
extradata += 8;
size = MPMIN(34, size - 8); // FLAC_STREAMINFO_SIZE
}
}
avp->extradata = av_mallocz(size + AV_INPUT_BUFFER_PADDING_SIZE);
if (!avp->extradata)
goto error;
avp->extradata_size = c->extradata_size;
memcpy(avp->extradata, c->extradata, avp->extradata_size);
avp->extradata_size = size;
memcpy(avp->extradata, extradata, size);
}
avp->bits_per_coded_sample = c->bits_per_coded_sample;