I am rendering project in Vegas which has three video tracks (on on top of another) and I just discovered how dumb rendering script vegas is using. It cost me a lot of wasted time because of that. What's the problem: when vegas is rendering video file which is on top it acts like it is analyzing the files beneath (it slows down greatly) even though the transparency of all 3 files is set to 100%. When I cut out some fragment of top and second video file and vegas is rendering bottom file its speed increases 2.5 fold. This is just insane; I remember years ago when I was experimenting with Premiere that it ignored files beneath. A simple change in the program code would allow smart rendering.

When I do multi-cam editing, rendering from SD-AVI to SD-AVI with NO effects, it just flies along ignoring the tracks beneath. Are you sure there's not something else going on? You sure the top track level is at 100%? No effects on the top track? No changes to track motion/track motion mode set to standard Alpha mode? If you wanted to post the VEG file, we could take a look to see if anything is obvious.