id,summary,reporter,owner,description,type,status,priority,component,version,resolution,keywords,cc,blockedby,blocking,reproduced,analyzed
1678,Regression with -vsync 1,jwjwjw,,"Summary of the bug:

It seems that the latest version of ffmpeg from git has a bug with -vsync 1. I re-encoded some footage from BBC television and the A/V sync slightly drifts over time which is noticeable with the lipsync being off, even though the original file has no sync issues. Using -vsync 1 has always fixed this in the past but it no longer works with the latest version of ffmpeg (N-43888-gfef9e84). It does, however, work with an earlier version, N-31890-gecaf514.

Included is a sample file (bbc1sample.mp4) as well as two ffmpeg output files, bbc1-ok.mov and bbc1-fail.mov, the 'ok' being encoded using N-31890-gecaf514 which is in perfect sync and the 'fail' being from the latest git master (N-43888-gfef9e84) which slowly drifts out of sync (I think it's out by around 0.1s in the sample media because I couldn't upload a larger clip, but as time goes by the sync gets worse and you can notice the lipsync is slightly off when the man is talking in vision). Both used identical ffmpeg options, just different ffmpeg versions.

However, playing the encoded file in QuickTime is fine. No sync issues. Using VLC or encoding to FLV and playing it in Flash does exhibit the sync issue. The original bbc1sample.mp4 plays fine in all players. Frame by frame visual comparisons between the 'ok' and 'fail' clips show a mismatch.

N-31890-gecaf514 results in a file with a duration of 00:00:49.64 and the latest version produces a file with a duration of 00:00:49.72. The sample outputs were encoded using libx264 and libfaac to reduce the file size but the problem occurs regardless of video or audio codec and the use or omission of -async has no effect either.

I have included log files which should hopefully shed more light on it.

How to reproduce:
{{{
% ffmpeg -i bbc1sample.mp4 -vb 300k -vsync 1 -async 1 -acodec libfaac -ab 192k -ac 2 -ar 44100 -vcodec mpeg4 bbc1-fail.mov
ffmpeg version N-43888-gfef9e84 Copyright (c) 2000-2012 the FFmpeg developers
  built on Aug 25 2012 01:37:52 with gcc 4.4.5 (Debian 4.4.5-8)
  configuration: --enable-libdc1394 --prefix=/usr --extra-cflags='-Wall -g ' --enable-shared --enable-libmp3lame --enable-gpl --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-avfilter --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-libvpx --extra-libs=-lgcrypt --disable-altivec --disable-armv5te --disable-armv6 --disable-vis
  libavutil      51. 70.100 / 51. 70.100
  libavcodec     54. 54.100 / 54. 54.100
  libavformat    54. 25.104 / 54. 25.104
  libavdevice    54.  2.100 / 54.  2.100
  libavfilter     3. 13.101 /  3. 13.101
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[h264 @ 0xf81a20] AVC: nal size 21839902
[h264 @ 0xf81a20] no frame!
[mov,mp4,m4a,3gp,3g2,mj2 @ 0xf7b240] max_analyze_duration 5000000 reached at 5022161
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'bbc1sample.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.25.104
  Duration: 00:00:49.58, start: 0.000000, bitrate: 900 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 640x360 [SAR 1:1 DAR 16:9], 798 kb/s, 28.27 fps, 25 tbr, 1k tbn, 50 tbc
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, s16, 93 kb/s
    Metadata:
      handler_name    : SoundHandler
-async is forwarded to lavfi similarly to -af aresample=min_comp=0.001:min_hard_comp=0.100000.
Output #0, mov, to 'bbc1-fail.mov':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.25.104
    Stream #0:0(und): Video: mpeg4 (mp4v / 0x7634706D), yuv420p, 640x360 [SAR 1:1 DAR 16:9], q=2-31, 300 kb/s, 25 tbn, 25 tbc
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, s16, 192 kb/s
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> mpeg4)
  Stream #0:1 -> #0:1 (aac -> libfaac)
Press [q] to stop, [?] for help
[h264 @ 0x12a07a0] AVC: nal size 21839902
    Last message repeated 1 times
[h264 @ 0x12a07a0] no frame!
Error while decoding stream #0:0: Operation not permitted
frame= 1243 fps=189 q=31.0 Lsize=    3069kB time=00:00:49.57 bitrate= 507.2kbits/s dup=1 drop=159    
video:2116kB audio:920kB subtitle:0 global headers:0kB muxing overhead 1.077261%
}}}",defect,closed,important,undetermined,git-master,fixed,regression,,,,0,0