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demux_mkv: parse FLAC channel layouts

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Handle a relatively recently introduced hack, that allows FLAC audio to
have arbitrary channel layouts, instead of just the predefined fixed
ones. This is actually supported by FFmpeg, but since the demuxer
(instead of the decoder) handles this in FFmpeg, we need to add special-
code to our mkv demuxer.

(The way FFmpeg does this seems a bit backwards, since now every demuxer
for a format that can handle FLAC needs to contain this logic as well.)

The FLAC hack is relatively terrible: we need to parse the FLAC headers,
look for a VorbisComment, parse the VorbisComment, and then retrieve
the magic WAVEFORMATEXTENSIBLE_CHANNEL_MASK entry. But the hack is
officially endorsed, as the official FLAC tools use it. (Although I
couldn't find a trace of it in the format specification. Should I be
surprised?)
This commit is contained in:
wm4 2015-07-20 12:48:41 +02:00
parent b0d1ac93cf
commit 3252d352c9
1 changed files with 67 additions and 0 deletions
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67
demux/demux_mkv.c
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@ -1345,6 +1345,72 @@ static int demux_mkv_open_video(demuxer_t *demuxer, mkv_track_t *track)
return 0;
}
// Parse VorbisComment and look for WAVEFORMATEXTENSIBLE_CHANNEL_MASK.
// Do not change *channels if nothing found or an error happens.
static void parse_vorbis_chmap(struct mp_chmap *channels, unsigned char *data,
int size)
{
// Skip the useless vendor string.
if (size < 4)
return;
uint32_t vendor_length = AV_RL32(data);
if (vendor_length + 4 > size) // also check for the next AV_RB32 below
return;
size -= vendor_length + 4;
data += vendor_length + 4;
uint32_t num_headers = AV_RL32(data);
size -= 4;
data += 4;
for (int n = 0; n < num_headers; n++) {
if (size < 4)
return;
uint32_t len = AV_RL32(data);
size -= 4;
data += 4;
if (len > size)
return;
if (len > 34 && !memcmp(data, "WAVEFORMATEXTENSIBLE_CHANNEL_MASK=", 34)) {
char smask[80];
snprintf(smask, sizeof(smask), "%.*s", (int)(len - 34), data + 34);
char *end = NULL;
uint32_t mask = strtol(smask, &end, 0);
if (!end || end[0])
mask = 0;
struct mp_chmap chmask = {0};
mp_chmap_from_waveext(&chmask, mask);
if (mp_chmap_is_valid(&chmask))
*channels = chmask;
}
size -= len;
data += len;
}
}
// Parse VorbisComment-in-FLAC and look for WAVEFORMATEXTENSIBLE_CHANNEL_MASK.
// Do not change *channels if nothing found or an error happens.
static void parse_flac_chmap(struct mp_chmap *channels, unsigned char *data,
int size)
{
// Skip FLAC header.
if (size < 4)
return;
data += 4;
size -= 4;
// Parse FLAC blocks...
while (size >= 4) {
unsigned btype = data[0] & 0x7F;
unsigned bsize = AV_RB24(data + 1);
data += 4;
size -= 4;
if (bsize > size)
return;
if (btype == 4) // VORBIS_COMMENT
parse_vorbis_chmap(channels, data, bsize);
data += bsize;
size -= bsize;
}
}
static const char *const mkv_audio_tags[][2] = {
{ "A_MPEG/L2", "mp3" },
{ "A_MPEG/L3", "mp3" },
@ -1547,6 +1613,7 @@ static int demux_mkv_open_audio(demuxer_t *demuxer, mkv_track_t *track)
extradata_len = size;
memcpy(extradata, ptr, size);
}
parse_flac_chmap(&sh_a->channels, extradata, extradata_len);
} else if (!strcmp(codec, "alac")) {
if (track->private_size) {
extradata_len = track->private_size + 12;