From b8c3a20f5e3d8b51a2528afdb129d3fac03ad9fd Mon Sep 17 00:00:00 2001
From: mplayer-svn <svn@mplayerhq.hu>
Date: Thu, 27 Oct 2011 20:09:09 +0000
Subject: [PATCH] demux_audo: fix wrong runtime and average bitrate for VBR MP3

Do so by determining the number of frames from the Xing/Info/VBRI
headers and by calculation a correct duration which leads to an
reasonable average bytes per seconds.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@34273 b3059339-0415-0410-9bf9-f77b7e298cf2
Author: ib
---
 libmpdemux/demux_audio.c | 68 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

diff --git a/libmpdemux/demux_audio.c b/libmpdemux/demux_audio.c
index e58bb55aae..d3720d2e24 100644
--- a/libmpdemux/demux_audio.c
+++ b/libmpdemux/demux_audio.c
@@ -257,6 +257,69 @@ get_flac_metadata (demuxer_t* demuxer)
 }
 #endif
 
+/**
+ * @brief Determine the number of frames of a file encoded with
+ *        variable bitrate mode (VBR).
+ *
+ * @param s stream to be read
+ * @param off offset in stream to start reading from
+ *
+ * @return 0 (error or no variable bitrate mode) or number of frames
+ */
+static unsigned int mp3_vbr_frames(stream_t *s, off_t off) {
+  static const int xing_offset[2][2] = {{32, 17}, {17, 9}};
+  unsigned int data;
+  unsigned char hdr[4];
+  int framesize, chans, spf, layer;
+
+  if ((s->flags & MP_STREAM_SEEK) == MP_STREAM_SEEK) {
+
+    if (!stream_seek(s, off)) return 0;
+
+    data = stream_read_dword(s);
+    hdr[0] = data >> 24;
+    hdr[1] = data >> 16;
+    hdr[2] = data >> 8;
+    hdr[3] = data;
+
+    if (!mp_check_mp3_header(data)) return 0;
+
+    framesize = mp_get_mp3_header(hdr, &chans, NULL, &spf, &layer, NULL);
+
+    if (framesize == -1 || layer != 3) return 0;
+
+    /* Xing / Info (at variable position: 32, 17 or 9 bytes after header) */
+
+    if (!stream_skip(s, xing_offset[spf < 1152][chans == 1])) return 0;
+
+    data = stream_read_dword(s);
+
+    if (data == MKBETAG('X','i','n','g') || data == MKBETAG('I','n','f','o')) {
+      data = stream_read_dword(s);
+
+      if (data & 0x1)                   // frames field is present
+        return stream_read_dword(s);    // frames
+    }
+
+    /* VBRI (at fixed position: 32 bytes after header) */
+
+    if (!stream_seek(s, off + 4 + 32)) return 0;
+
+    data = stream_read_dword(s);
+
+    if (data == MKBETAG('V','B','R','I')) {
+      data = stream_read_word(s);
+
+      if (data == 1) {                       // check version
+        if (!stream_skip(s, 8)) return 0;    // skip delay, quality and bytes
+        return stream_read_dword(s);         // frames
+      }
+    }
+  }
+
+  return 0;
+}
+
 static int demux_audio_open(demuxer_t* demuxer) {
   stream_t *s;
   sh_audio_t* sh_audio;
@@ -266,6 +329,7 @@ static int demux_audio_open(demuxer_t* demuxer) {
   // mp3_hdrs list is sorted first by next_frame_pos and then by frame_pos
   mp3_hdr_t *mp3_hdrs = NULL, *mp3_found = NULL;
   da_priv_t* priv;
+  double duration;
 
   s = demuxer->stream;
 
@@ -342,7 +406,7 @@ static int demux_audio_open(demuxer_t* demuxer) {
     sh_audio->wf->nBlockAlign = mp3_found->mpa_spf;
     sh_audio->wf->wBitsPerSample = 16;
     sh_audio->wf->cbSize = 0;
-    sh_audio->i_bps = sh_audio->wf->nAvgBytesPerSec;
+    duration = (double) mp3_vbr_frames(s, demuxer->movi_start) * mp3_found->mpa_spf / mp3_found->mp3_freq;
     free(mp3_found);
     mp3_found = NULL;
     if(s->end_pos && (s->flags & MP_STREAM_SEEK) == MP_STREAM_SEEK) {
@@ -378,6 +442,8 @@ static int demux_audio_open(demuxer_t* demuxer) {
 	demux_info_add(demuxer,"Genre",genres[g]);
       }
     }
+    if (duration && demuxer->movi_end && demuxer->movi_end > demuxer->movi_start) sh_audio->wf->nAvgBytesPerSec = (demuxer->movi_end - demuxer->movi_start) / duration;
+    sh_audio->i_bps = sh_audio->wf->nAvgBytesPerSec;
     break;
   case WAV: {
     unsigned int chunk_type;