My daughter has a new Wellcom 819 cellphone with MP4. It had some MP4 files from Wellcom on it, and they play okay both on the phone and my computer with any of my players. However, when I try to play my own MP4 files on the phone, it errors with 'invalid format'. I've created those MP4 files from AVI or FLV files with various programs including VLC, and with VLC even tried new copies with the same codex (mp4v) and any other characteristics I could identify but to no avail. Neither can I see anything different between the files from Wellcom that do play and mine that don't.

Any ideas on how I can get the phone to play my MP4 files would be appreciated.

There are MP4 variations. Try an MP4 AAC setting. Modern media players and mobile phones support the AAC standard.

There are MP4 variations. Try an MP4 AAC setting. Modern media players and mobile phones support the AAC standard.

Yeah, I tried that. Thanks, anyway.