Cutting avi video with ffmpeg, audio doesn't sync

[aspidistra]

Command :

ffmpeg -ss 00:54:10 -t 00:03:04 -i movie.avi -acodec copy -vcodec copy output.avi

gives me un-synced audio/video (when the file 'movie.avi' is synced). Why is that?

How to cut with perfect sync.

[andrew.46]

There may be some hints in the complete terminal output, including the commandline. Can you copy and paste this into a Forum post?

[aspidistra]

There may be some hints in the complete terminal output, including the commandline. Can you copy and paste this into a Forum post?

ffmpeg -ss 00:54:10 -t 00:03:04 -i outpost11.avi -acodec copy -vcodec copy oooo.avi
ffmpeg version 0.8.10-4:0.8.10-0ubuntu0.12.04.1, Copyright (c) 2000-2013 the Libav developers
built on Feb 6 2014 20:56:59 with gcc 4.6.3
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a future release. Please use avconv instead.
[mpeg4 @ 0x13a79a0] Invalid and inefficient vfw-avi packed B frames detected
Input #0, avi, from 'outpost.avi':
Duration: 01:30:10.04, start: 0.000000, bitrate: 1081 kb/s
Stream #0.0: Video: mpeg4 (Advanced Simple Profile), yuv420p, 640x272 [PAR 1:1 DAR 40:17], 25 tbr, 25 tbn, 25 tbc
Stream #0.1: Audio: mp3, 48000 Hz, stereo, s16, 128 kb/s
Output #0, avi, to 'oooo.avi':
Metadata:
ISFT : Lavf53.21.1
Stream #0.0: Video: mpeg4, yuv420p, 640x272 [PAR 1:1 DAR 40:17], q=2-31, 25 tbn, 25 tbc
Stream #0.1: Audio: libmp3lame, 48000 Hz, stereo, 128 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Stream #0.1 -> #0.1
Press ctrl-c to stop encoding
[NULL @ 0x13a79a0] Invalid and inefficient vfw-avi packed B frames detected
frame= 4672 fps= 0 q=-1.0 Lsize= 17080kB time=184.01 bitrate= 760.4kbits/s
video:13866kB audio:2911kB global headers:0kB muxing overhead 1.804645%

[andrew.46]

Hmmm.... the only error there is a complaint from FFmpeg that a hack has been used to push b frames into an avi container and usually this is a cautionary warning only. Does the following command make any difference:

ffmpeg -i -ss 00:52:10 outpost11.avi -ss 00:02:00 -t 00:03:04 -codec copy test.avi

If not perhaps you may have to actually reencode the video stream. Some interesting reading here. You would probably also be well served by upgrading your copy of FFmpeg as detailed elsewhere on this excellent wiki...

Edit: See the cautionary note on the wiki page a linked to:

Doing a bitstream copy gives me a broken file?

If you use -ss with -c:v copy, the resulting bitstream might end up being choppy, 
not playable, or out of sync with the audio stream, since ffmpeg is forced to 
only use/split on i-frames.

[aspidistra]

will try it

command doesn't seeem to work

when i've tried it again i'll get back to you

thanks

[SeijiSensei]

You could try mencoder for this task. It's pretty old now but was developed originally to handle the AVI container. You can install it from the repositories with "sudo apt-get install mencoder".

I ran a little test with an AVI encoded with DivX and MP3 and had audio syncing problems as well. However you can adjust the synchronization with the "-delay" parameter. I'd be surprised if ffmpeg didn't have the same type of option.

Andrew, do you suppose this has to do with not cutting exactly on a keyframe?

[andrew.46]

Andrew, do you suppose this has to do with not cutting exactly on a keyframe?

I have to confess I am no expert in this issue and thus I would only be guessing .