The files, well at least AMV files are definately compressed.
A single image from an AMV clip really looks close to a strongly jpg-compressed image ! And if you extract the frames from a short avi or mpg clip, batch-convert them to compressed 96x64 jpg's you'll obtain an average of 3-5 ko/pic.
5x16x60= 4800 ko/min
I compressed the jpg's with Irfan View, using a quality rate of 30, which is the littlest possible without alterating too much the pics.
The point is that AMV files are 2000-2200 ko/min max. So.... I don't know how they are compressed...