I'm not sure if "empty" is the correct term for it but, i'm rendering a MP4 Mainconcept video at 720p, Main profile, 30,0 fps, Constant Bit rate of 30.000.000 audio at 44.100mhz and 256 bits.
It took 2 hours to render a 10 min video and when i open the finished video, NOTHING HAPPENS, it just won't play. I take a look with media info and the file basically don't show any kind of info, no frame rate, no screen size, no bit rate, just tell me it's a MP4 file. I really have no ideia what might be happening.
We don't either until you provide some very basic information including source material (frame size/rate, codec, etc.) project settings (project size, frame rate, etc.) and render settings much like you've stated. Rather than words, it's more precise to simply do a screen shot of these property windows and upload them. A screen shot of your timeline can also be of great assistance. For example, here are shots of the three property windows I mentioned.
First your media properties. (Select event. Right-click. Select Properties. Then, Media Tab)
Then, project settings. (Alt-enter)
And finally, render settings. (Select Render Template, then Customize Template)
The more information that you provide, the more likely someone will be able to help.
Did you have a loop region defined? There is a check box in the render screen that tells Vegas to render only the loop region. Depending on your version of Vegas, if the option is checked, and the loop region is very small or non-existant, the rendered output can be absent.