Video accessibility is a hot subject at this moment. The ministry web sites over here use a custom made player based on Jeroen Wijering’s FLV Media Player. The player supports audio descriptions and captions. It tests if the visitor has JavaScript combined with Flash, Quicktime or WMP; and if so it displays a player for that. If not, a text alternative is displayed.

Some interesting pages that extremely well illustrate the possibilities of all this: Description of the video player (and an English variant, a bit less detailed); Making video accessible.