We recommend the MPEG4 (Divx, Xvid) format at 320x240 resolution with MP3 audio. Resizing your video to these specifications before uploading will help your clips look better on YouTube.
320x240. 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.
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Google Answers: two simple YouTube (or similar) questions
http://www.youtube.com/t/help_makevideo
Making Movies: YouTube and the Flash video format
