Mark Pilgrim has written a book called HTML5: Up & Running. It is available in a variety of formats and if you gronk that HTML jive you probably should buy a copy.
This is an chapter from the book. Before the web hosting services folks had to have the right media player to watch videos. It was a problem. Not only about bandwidth and pixelation but how where you gonna see the video?
There was RealPlayer RM, RAM, QuickTime .mov Windows .avi and .wmv and you never knew when you went to a web site what would be required. Adobe Flash and Flash video solved a lot of problems and created a few of its own.
There are new concerns now. This chapter is for the tech savvy who really understands the behind the scene action on encoding, compression, HTML and video file formats/containers.