From 8862fb41e0f1ce7d0dbb93008c2bedf659c40f15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andreas=20=C3=96man?= <andreas@lonelycoder.com>
Date: Wed, 24 Oct 2007 04:56:22 +0000
Subject: [PATCH] add support for reading duration from VBRI-tag in mp3 files
Originally committed as revision 10851 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
libavformat/mp3.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/libavformat/mp3.c b/libavformat/mp3.c
index 7781bd93819..9a0b020f2ff 100644
--- a/libavformat/mp3.c
+++ b/libavformat/mp3.c
@@ -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 */
--
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