Hello from the from the mess that is the Droid Bionic forums! I had the chance to play with and setup email on a co-worker's Infuse today, nice phone!
I currently have a Droid Charge and have put some HD videos on it, they were LIFE blu-ray disc rips, they would play but i did not get any sound. Here is a couple things I learned:
1. The Android OS runs the SD card only in FAT32 and FAT32 can only have files of 3.5 gig or smaller (or close to that), most HD videos/movies are more than this
2. Android also cannot decode HD codecs, like DTS HD or AC3, which is why if you do have a video that can "fit" on the SD card that is HD in .MKV format it still won't play the sound. :'(
I do have "Sucker Punch" in HD in .AVI format on my SD card and it plays sound, so it can play HD videos/movies with sound they just have to be in a different format than .MKV and have a codec that the media player can decode. I would also note there are some media players on the android market that are supposed to play .MKV with sound as they can decode the audio but the free trial one i tried, although nice looking, was very laggy and did not play the audio, but there may be a free or paid one out there.
Hope this helps.