I have psp 3.03oe-c and when i added a video(mp4) and when i click on it...it says "file not supported" i triedd putting it in the VIDEO folder and then also in the MPROOT/100MNV01 folder....??? but still nothing worked...i've looked around but no answers thats why i had to add another post in here..maybe i can get some answers....thank you for your time.

did you rename it when you put it in 100mnv01 folder, should be renamed M4vxxxxx.mp4 xs being numbers.

it could also be MAQ in steap of the M4V. try replaceing the first 3 letters, with eother one of those, and make sure their is 5 #'s only.

Most likely the video was compressed into the wrong resolution, like he mentioned it worked with other files.
you would have to recompress it to the right resolution.

You need to get the filename and directory structure right.
If putting it in "ms:\VIDEO\" doesn't work then, you will need to put it in:
"ms:\MP_ROOT\100MNV01\" (for non AVC) and rename it to "M4V#####.MP4"
"ms:\MP_ROOT\100ANV01\" (for AVC) and rename it to "MAQ#####.MP4"

i've tried renaming it to M4V but it still doesnt work. they are all "MAQ" so i guess this are compressed files right? so what would i have to do to be able to play them right? is there some kind of program i can use to fix this? thanks for all your help guys.