I am able to play MP4 and AVI and the size of the file ranges from 700mb to 2.4gb. I had 2 films both 720p and both were in MP4 format. Film A was 2.5gb and playback was fine on stock player. However Film B was 2.1gb and the player kept lagging badly, forcing me to exit and close down the app. I think there are quite a few variants when it comes to video files, it could be the way the video was compressed or encoded?
What are the videos... recorded from a personal source (camcorder etc) or feature length videos?
The problem wiganblue has is that the videos work on his phone...from the internal storage only. If wiganblue tries to playback a video from the external it screws up.