OSX4.8/G5/dual/2.0ghz/2gigRAM/

I have a few ***** ******* videos downloaded. Some, when I try to play through MPlayerOSX, sound like metal scratching across a metal surface.

Is this a case of me not playing the movie at the correct setting?
Is there a way to convert the movie to play. Some begin fine, then break into the screeching.

jr
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