Youtube is pretty specific about what it likes these days.
container: mp4
video: h.264
-high profile
-30fps only, 60 isn't allowed at any resolution now
audio: aac-lc
-up to 512khz is supported
After that you just need to get the video bitrate under control. Vegas' presets tend to be either way too high or too low for the resolution. 3000kbps is generally ok for 720p videos, but 5000kbps will look better if you don't mind the larger file.
If you want 1080 then you should be looking at around 6000kbps, 8000kbps being better.
Keep in mind that old Vegas had a bad h.264 encoder (TBH the current ones aren't exactly great) so you may still run into problems.
Last edited by SkulFuk; Apr 19, 2013 at 07:26 PM.
Reason: just spotted a typo :s