Vegas pro file size explosion - having to use Handbrake currently
The easy answer is to analyze the resulting files in order to determine what's happening. mediainfo is a multi-platform open source tool that will help you do exactly that. Handbrake is likely using a much lower bitrate by default than Sony Vegas Pro. If I'm not mistaken, the standard settings for SVP are pretty high. You can prove this to yourself with the aforementioned mediainfo tool, and then solve it by adjusting the SVP bitrate settings accordingly.