Having problems playing mp4 movies on my psp?

[jwblu]

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