Are all videos out of synch? I've got a crummy digitizer and some software I got for free after rebate. After recording half an hour of video, the audio and video are no longer aligned and editing the captured video doesn't help. Others could be using crummy tools as well. Could you have simply picked poor quality material?
Viewers depend on codecs to decypher video files. You may need to download a new codec.
There are several other viewer programs. I like Xine.