Also RealPlayer. It’s a free program. And it works with both Internet Explorer and Firefox. It also has a converter to for converting YouTube video’s .flv format to .mwv, so you can watch them on Windows Media and elsewhere.
Interesting piece on YouTube’s .flv video format...
YouTube and the Flash video format:
I’ve been trying to figure out why the quality of some videos suffers so greatly after being uploaded to YouTube. Here’s what I’ve learned.
When you upload a video to YouTube, it is transcoded (decoded to raw video, then re-encoded) into Flash Video (FLV) format. The video frame size is scaled to no larger than 320×240. I haven’t been able to tell exactly what the rates are, but the frame rate appears to be between 25 and 30 frames per second, and the video data rate appears to be somewhere around 200 Kilobits (kbps) per second. Audio is reduced to mono and transcoded to a lower bit rate. This transcoding is what’s going on in between the time you complete your upload to YouTube, and the time that the video is finally available for viewing.
200 kpbs is an exceptionally low data rate for video. By comparison, typical DVD rates are around 8 Megabits per second (mbps), and DV video has a rate of 25 mbps. Of course, these formats have over four times as many pixels as a YouTube video. Computing the data rate on a per-pixel basis, DVD video has a data rate about 9 times greater than the FLV format used at YouTube, and DV video has a data rate nearly 28 times greater. ...”
Lots more at link:
http://blog.chron.com/makingmovies/2006/04/youtube-and-the-flash-video-format/