I'd like to bump this to the top and add a bit of info, perhaps other know more.
Took some time to find that the Evo 4G (previous gen) suppoted .mp4 files meeting IMSA format standards and containing h.264 video with AVC Level 3.1 and below, 720p max resolution, AAC stereo audio. No AC3 or DTS.
This severely limits its usefulness as a mobile video player when traveling.
Got my MHL cable and can confirm that vids coded as above for the 4G also play on the 3D. They also work out the hdmi port to several tvs that I have tried.
Need to know what codecs the 3D can support. Recoding video to the above very non-standard set of parameters is a PIA. Surely this information is published somewhere....
And before any one else suggests rockplayer or V-player, the do not add ANY additional HD capabilities the built in player does not have. The phone will only play in HD what it can process on its hardware based decoder. Software decoders just are too processor intensive and don't work. Bought them, tried them wasted the money.