The screen resolution is 320x240, so something close to that would work best.
I'm about 90% sure it supports WMA too.
Frame Rate does not have to be 15 FPS. I know for a fact that 30 FPS works great.
The things that really affect whether or not your file will work, are the bitrate and codec. You will have to play around with bit rates until you find one that works. The reason the included arcsoft program is nice is because it will always spit out a supported bitrate. You might want to use that if possible to test and see what settings a file that was converted with it has, and try to emulate that with your program.
The other thing that is big problem is the codec used to encode the file. Just because the file says .mp4 doesn't mean the pilot will recognize it. Different programs encode with different codecs, so you'll have to try different programs to find one that is supported. That's why it's usually best to stick with a program people have tested and know works.
Check out this post. The video part should also work fine in Windows, and maybe on a Mac:
http://www.insigniaforums.com/index.php/topic,16.0.html