getting movies captured from kmplayer to play on a sony psp?

I don’t know why thy wont play in the mp4 format on my psp, but the psp says its not supported, This is how Im getting the files and putting them in. 1- Capture video in kmplayer under mp4 and at default settings. 2- Then use psp video manager to put file in my psp under root file. 3- In psp under movies there is a ? icon for the file, try to play and says file not supported and my firmware is 3.73 I’ve tried everything I can think of to make it work, any help would be nice. thank you