I've seen this before with movie files that had not much keyframes
bsplayer is not really frozen but it takes him/the codec a looonng time to decode the video to the place you switch to, much more than if the file had a decent keyframes/deltaframes ratio; that's normal (for a quick explanation about keyframes and deltaframes, see
this page on divx.com)
1. Have you tried to play these movie files with different players, were the results the same ?
2. I think many tools exist to check the keyframes amount (amongst other parameters) but I don't remember the names right now.
I know virtualDub does it (file->avi information I think)
usually you should have at least one keyframe every 10 seconds. If you find the video has only 3 keyframes in 40mns, there is definitely a problem with the file (corrupt/badly encoded)