I just noticed that Youtube says 'HTML 5 player' instead of 'Flash player'.
"YouTube's video pick spells doom for Adobe Flash"
http://www.cnet.com/news/youtubes-html5-video-a-big-nail-in-flash-coffin/
Here you can still choose which standard you want to use for your browser:
https://www.youtube.com/html5
I wonder if the Vegas render template for Youtube would change by this?
Not sure if they are still using H.264 for the HTML5 player.
Try switching the player standard, the video of the HTML5 version looks and sounds more cleaner even at 360p.
VMP