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matroskadec: Implement support for ALAC

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This patch implements support reading ALAC from Matroska files. The
only non-trivial thing about it is that only the ALAC magic cookie is
stored in Matroska's CodecPrivate element but not the "atom size",
"tag" and "tag version" fields that FFMPEG's ALAC decoder
expects. However, those are trivial to re-create.

Sample files are available:
http://www.bunkus.org/videotools/mkvtoolnix/samples/alac/alac-in-matroska.mka
and the CoreAudio file it was created from with today's mkvmerge:
http://www.bunkus.org/videotools/mkvtoolnix/samples/alac/alac-in-matroska-source.caf

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Moritz Bunkus 2012-08-05 16:25:48 +02:00 • committed by Michael Niedermayer
parent d106ffd942
commit bc3b422029
2 changed files with 13 additions and 0 deletions
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1
libavformat/matroska.c
View file

@ -24,6 +24,7 @@
const CodecTags ff_mkv_codec_tags[]={
{"A_AAC" , CODEC_ID_AAC},
{"A_AC3" , CODEC_ID_AC3},
{"A_ALAC" , CODEC_ID_ALAC},
{"A_DTS" , CODEC_ID_DTS},
{"A_EAC3" , CODEC_ID_EAC3},
{"A_FLAC" , CODEC_ID_FLAC},

12
libavformat/matroskadec.c
View file

@ -1580,6 +1580,18 @@ static int matroska_read_header(AVFormatContext *s)
&& (track->codec_priv.data != NULL)) {
fourcc = AV_RL32(track->codec_priv.data);
codec_id = ff_codec_get_id(ff_codec_movvideo_tags, fourcc);
} else if (codec_id == CODEC_ID_ALAC && track->codec_priv.size) {
/* Only ALAC's magic cookie is stored in Matroska's track headers.
Create the "atom size", "tag", and "tag version" fields the
decoder expects manually. */
extradata_size = 12 + track->codec_priv.size;
extradata = av_mallocz(extradata_size);
if (extradata == NULL)
return AVERROR(ENOMEM);
AV_WB32(extradata, extradata_size);
memcpy(&extradata[4], "alac", 4);
AV_WB32(&extradata[8], 0);
memcpy(&extradata[12], track->codec_priv.data, track->codec_priv.size);
} else if (codec_id == CODEC_ID_PCM_S16BE) {
switch (track->audio.bitdepth) {
case 8: codec_id = CODEC_ID_PCM_U8; break;