OK, I have an episode of Seinfeld in AVI format. It is around 175 megs in size. I have tried to play it on the GP2X adn it plays e series of still frames.

Do I have to reformat the AVI file so it plays back at a lower resolution?

I would have thought the GP2X would play any file as long as it was supported?

I believe your problem might just be with the file in general. Avi is just a container. The file inside could be just about anything. Xvid/mpeg1/2/4, Divx1-5, asf??? The file size would seem to indicate that the source file was a large bulky one probably divx 1-2 which isnt supported by GP2X. For instance, I have multiple Seinfeld episodes in divx 5/avi format and they clock in at about 45-60 megs in avi. These episodes do play just fine in my GP2X even though a strait mpeg 1 or 2/avi wont. Gp2x seems to do best with Divx 3 and above or Xvid/avi.

All is not lost however, as any format should be able to be easily converted. If your using Windows, download PocketDivx. When prompted choose Iriver p100 device which is 320x240 resolution which is the same as the GP2X. Click the the advanced settings tab on the bottom, and choose VHQ/Xvid and convert. I have never had a file not work after using this feature. The kicker is that once reformatted to the GP2X screen, a 700 mb Dvx/Xvid full movie file shrinks down to under 200 mb saving room on your card, and your battery life due to less proccesor work with rescaling.

Technically, the CPU doesn't worry about this, the Scaler does. But the scaler does take a hideous toll on battery life; so rescaling the video to 320x240 before copying it to your SD card is indeed quite crucial.

i think the problem could be the usage of Xvid. If the video was encoded with "Global Motion Compensation", Quarterpel and B-frames on, than it's normal for the GP2X to show only the keyframes or stutter the whole time. E.g. with GMC an Qarterpel encoded movies don't run on my standalone DVD-Player (it runs normal Xvids) and my old PC (Athlon XP 2400+) is stressed quite a bit by playing the files.