if you upload 720p, it'll always provide an option for lower quality anyway
here's a short list off the top of my head for all the "&fmt" stuff
* &fmt=18 = ipod/iphone h264/aac->mp4-compatible quality - typically up to 480
vertical, meaning:
- 480x272 mp4 (widescreen) OR 480x360 mp4 (fullscreen)
* &fmt=22 = HD 720p h264/aac->mp4, up to 720
horizontal lines, meaning:
- 1280x720 mp4 (widescreen) OR 960x720 mp4 (full screen)
* &fmt=34 = h264/aac->flv container. i believe max vertical lines is 400, so
- 400x222 flv (widescreen) OR 400x300 flv (full screen)
* &fmt=35 = h264/aac->flv container, HQ. i believe max horizontal lines is 480, so
- 848x480 flv (widescreen) OR 640x480 flv (full screen)
* &fmt=37 = h264/aac->mp4 1080p (*NEW!* this week). 1920x1080p in mp4.
- example:
http://www.youtube.com/watch?v=5f-MYl-HzNw&fmt=37
use a downloadhelper firefox plugin to verify results