I have to extract a thumbnail from a video (from url) and I use this code:
NSString *stringUrl = video.stringurl;
NSURL *url = [NSURL URLWithString:stringUrl
on one of my app i've captured an image from the video url like this:
MPMoviePlayerController *player = [[[MPMoviePlayerController alloc] initWithContentURL:videoURL]autorelease];
UIImage *thumbnail = [player thumbnailImageAtTime:0.0 timeOption:MPMovieTimeOptionNearestKeyFrame];
just passing the url object as videoURL and with the use of MPMoviePlayerController i successfully able to have the image all the time. hope you too will be able to do this with this simple code