[Ffmpeg-devel] seek with duration for cutting: broken or changed?

Cyrus A lists
Mon Oct 30 18:55:16 CET 2006

The following command used to work to cut a specific segment out of a 
video file on some FC3 machines I'm using with an old version of ffmpeg 
(still does work):

ffmpeg -acodec copy -vcodec copy -i fullvideo.avi -ss 60 -t 120 

But it doesn't work anymore with Fedora Core 5 on a 64-bit machine 
running today's SVN copy of ffmpeg. (Also doesn't work with freshrpms 
latest ffmpeg rpm, either.) I believe what it's doing is seeking, but 
the duration is completely ignored. It just returns the rest of the file 
from where the seek took it. The resulting file is also a little 
"chirpy"  -- the audio video sync is messed up somehow.

If I take out the "-acodec copy" and "-vcodec copy" options, it performs 
correctly, except it re-encodes the video instead of just copying the 
data bit by bit with no reprocessing (which is much faster). That is, 
the seek and duration params work as they should, but it re-encodes 
rather than giving a direct stream copy. I'd like to get back to having 
seek and duration work while doing a direct stream copy.

Anyone know why this has happened? Did the seek or duration options 
change? Why would copying vs. reencoding matter?


More information about the ffmpeg-devel mailing list