[FFmpeg-user] -istoffset and -vcodec copy

[Jonathan Addleman]

Hello,

I'm trying to fix a video with an out-of-sync audio track. You can see 
the file in its current state at youtube - 
http://www.youtube.com/watch?v=F1jv6V5aYGk

Here's the command line I've tried: ffmpeg -g 1 -i F1jv6V5aYGk.mp4 
-itsoffset 0.5 -i F1jv6V5aYGk.mp4 -map 1:0 -map 0:1 -vcodec copy -acodec 
copy fixed.mp4

Unfortunately, the itsoffset command is completely ignored in this case 
- the 'fixed' video has the same out-of-sync audio as the original.

However, if I re-encode the video by removing '-vcodec copy' from the 
commandline, the itsoffset works as expected. Of course, I don't want to 
re-encode the video, since it reduces the quality too much.

I've also tried adding -async 1, but did not see any effect.

Is this a bug in ffmpeg? Or am I misunderstanding how this command 
should work? Thanks!

-- 
Jon-o Addleman - http://www.redowl.ca