I found two programs that are able to convert video files to 3gp and work for my mpm player. I have this player:
gallery
A simple program is Kagun video converter and can be found here:
kagun video converter
The second one is more complicated and called SUPER © Simplified Universal Player Encoder & Renderer. and can be found here:
super encoder
for my player I use the following settings:
Video:
output container: 3gp (sony ericsson)
video codec: mpeg4
video scale size: 320.240
aspect ratio: 16:9
video bitrate: 432
Audio:
sampling: 44100
channels: 2
bitrate: 128
Dont download the program from the authors page, the file is corrupted. Use some download site (google).
good luck,
Leo.