For the last few weeks, some MPG files, will be like say 39 seconds long. After 39 seconds they stop playing, but if I like go back to the 11 second marker or something, it will play parts that should be after the 39 second area. If I keep going back, and doing this, I can watch the whole clip, but its pointless, and not even fun to watch.

Anyone know what this is? Or how to fix it? I am preety sure I have all the newest codecs, as that hasn't been a problem.