Bizarre sync issue

[cinesimon]

Hello there!
I am hoping someone here can help.

I recently got a copy of a film, ripped from a Bluray(the audio and video sources may have been different, I really can't say) in avi format.
On my computer, both on vlc and wmp, it plays fine.
However on my WDTV media player, it plays out of sync badly - initially it's only very slight, but soon it gets worse and worse.
It's as if the audio and video are different formats: one PAL, the other NTSC - or something like that.
Except in cases where I have seen and fixed this before, it has shown up on the computer, and was easily fixed changing the format of the video file using mkvmerge. Obviously I can't do that in this case, as the computer doesn't show a problem!

So, I'm hoping someone with more knowledge than I can help with this.

Thanks in advance,
Simon

[cinesimon]

Actually I just figured it out - put it through mkvmerge, compression for both audio and video set to 'none', converting the avi to an mkv of course - it now plays perfectly.
S.