These are the YouTube Specifications on their web site:
Resolution: 1280 x 720 px or 640 x 480 px
Bit Rate Optimize for resolution, aspect Ratio, frame rate (not bit rate)
Frame Rate: TBD
Codec: H.264, MPEG-2 or MPEG 4
Audio: MP3 or AAC
Sample Rate: 44.1 kHz
Channel: 2 (Stereo)
Length: 10 min (There is a exception to this, but if you create a video longer it better be a major motion picture)
File size: 100 meg max (So far)
This seems to be the important technical aspects I have briefly found. Please add to this list if you think it is important.