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add support for reading duration from VBRI-tag in mp3 files 

Originally committed as revision 10851 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Andreas Öman 2007-10-24 04:56:22 +00:00
parent 3a1d358825
commit 8862fb41e0
1 changed files with 15 additions and 3 deletions
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18
libavformat/mp3.c
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@ -426,9 +426,9 @@ static int mp3_read_probe(AVProbeData *p)
}
/**
* Try to extract a xing tag from the stream and if found, decode it
* Try to find Xing/Info/VBRI tags and compute duration from info therein
*/
static void mp3_parse_xing(AVFormatContext *s, AVStream *st)
static void mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, offset_t base)
{
uint32_t v, spf;
int frames = -1; /* Total number of frames in file */
@ -448,6 +448,18 @@ static void mp3_parse_xing(AVFormatContext *s, AVStream *st)
frames = get_be32(&s->pb);
}
/* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
url_fseek(&s->pb, base + 4 + 32, SEEK_SET);
v = get_be32(&s->pb);
if(v == MKBETAG('V', 'B', 'R', 'I')) {
/* Check tag version */
if(get_be16(&s->pb) == 1) {
/* skip delay, quality and total bytes */
url_fseek(&s->pb, 8, SEEK_CUR);
frames = get_be32(&s->pb);
}
}
if(frames < 0)
return;
@ -503,7 +515,7 @@ static int mp3_read_header(AVFormatContext *s,
}
off = url_ftell(&s->pb);
mp3_parse_xing(s, st);
mp3_parse_vbr_tags(s, st, off);
url_fseek(&s->pb, off, SEEK_SET);
/* the parameters will be extracted from the compressed bitstream */