in regard to answer 2, it doesn't matter what size, if they are only gonna be played on computers. what matters is the bit-rate, in terms of choppy playback on slow machines, or with poorly-designed OS that make excessive use of virtual memory. the one they often use to cut down the bit-rate and still get something that isn't too pixellated is divx, but there may be an hundred competing codecs by now FAIK, each one having its adherents as to why it's superior. the one they use on commercial dvds is sometimes called mpeg-2, and it uses vob files as a way to compress about an hour of video onto 2 GB of disk space. in that case, the pixel size of the frame does matter, but then it's for playback on non-computers.