FWIW vi does run on plan9 - fgb did a curses port and vim runs under that, various people turn in their graves if you try to use it however.
there is also a lockable screensaver called screenlock(1) what kind of MPEG support do you want? Audio support is not bad, I have a port of an aac audio decoder and there is mp3 encoders and decoders. Mpeg2 video should not be too hard, Mpeg4, H264, etc are nastier but where do you stop. there is a new encoding standard per month these days. -Steve
