I like to use my Roku2 to play mp3 music files off a usb flash drive.
It will play through them in order, or I can turn on random shuffle.
I also have a bunch of mp4 music videos, but when I try to play them it makes my select and play each one individually. This is not nearly as convenient as playing the mp3 files (actually, it's so much work, I don't generally even do it). I would really love if I could play my mp4's as easily as I can play my mp3's.
I guess most people's mp4 videos are longer, but since mine are ~4 minute music videos, it's really cumbersome to select/play a new file every 4 minutes :\