Hello, Sorry, I sent the message to early... I'm not quite sure if I found a bug in the QuickTime demuxer of mencoder. I cut off of some parts of a movie encoded with libavcodecs mpeg4 codec and saved it as self contained QuickTime movie. After that I wanted to compress it a little more using the xvid codec included in mencoder. But now the video track does no more start with a key frame. mencoder prints some error messages and the image gets heavily damaged. I think the problem might be that each QuickTime track contains a media describing the video. the media begins with a keyframe (though i'm not quite sure about that) but the track maps the media in its own time-coordinatespace, not necessarily beginning with the first frame of the media it contains, so the track does not begin with a key frame. Is this scenario possible? The sample movie is about 350 MB, but perhaps I can make a little samplemovie with the same problem if this could help. Another Problem is I cannot make the movie public since I got no access to a public server. Is there anything else you have to know? Regards Christoph