The YouTube Video Toolbox at http://www.youtube.com/t/howto_makevideo
says:
"Uploading Your Videos to YouTube"
"Once you're happy with your final result, you'll need to save the video in
a format that YouTube can accept in order to upload. Unless you're a professional
video producer, we recommend that you save your videos as either QuickTime .MOV,
Windows .AVI, or .MPG files– these are the most common formats and they work well
within our system. We specifically 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."
Got that???
If you are an Apple iMovie HD user, you may find the following instructions a lot
clearer:
iMovie HD
In iMovie, select File>Export>QuickTime. Compress movie for: Expert Settings.
Share. Export: Movie to Quicktime Movie>Options. Video>Settings: MPEG-4 Video,
30 frames per second, Key frames: Automatic, Compression: medium quality. Data rate:
Automatic. Size>Dimensions: 320 x 240 QVGA. Save sound as AAC, 44.1Khz, mono,
Quality:Normal, Target bit rate: 64 kbps
Frederick L. Shippey, Electronic Imaging Consulting, 24 January 2007