Playing video files on 8800

Hi, I've copied some music video files to the 8800 from iTunes using BB DeskTop s/w.

These files play ok on my PlayBook - so DRM is not an issue.

They are .M4V video files about 47 Meg each.

When I try to play on my 8800 I get a green flash for a split second that says "Loading" in the top right hand corner of the video player screen - then the file plays BUT only the audio - not the video.

When I look in properties in the 8800's media browser it says the file type is .MP4 (which seems odd) - unless BB DeskTop has converted them somehow?

1) Am I just missing a codec? If so, how do I get the codec and install it into my 8800?
2) If I go into "options" in media player on the 8800 there is a setting that says "Device Memory Limit 5MB" and I only have options to increase this to 10MB or 15MB - certainly nothing like the circa 50MB I'd need - could that be something to do with it?
3) Or, can an 8800 not play this type (or size) of video file?
4) Does BB DeskTop convert .M4V files to .MP4?

Thank you!

Harry