I have an mp4 that wont play on my WD TV HD Media Player. Is there a way to convert it to a more universal format (perhaps just MKV?) without losing the quality and sound.

Here is the mp4 info:

General
BDAV: 5.02 GiB. 1h 38mn
1 Video stream: AVC
1 Audio stream: AC-3

Video
6379 Kbps, 1920x800 (2.40.1), at 23.976 fps, AVC (High@L4.1) (CABAC / 4 Ref Frames)

Audio
640 Kbps, 48.0 KHz, 6 channels, AC-3

I have iSkysoft Media Converter