I always use .mov format with PNG compression. That preserves the alpha in the render, although you do need to set it manually next time you use it in Vegas. PNG is kind of cool in this instance since the alpha layer compresses way down and yet the talking head part is lossless. Preview isn't very smooth, but aside from that it works well.

Does anyone have a better way to do this? Only the expensive versions of Cineform do an alpha layer, so the PNG .mov is the best one I know of. I'd love something that previews a little more smoothly though.

I used the "premultiplied" alpha setting.
And also sent along another file which was "unmatted".
Haven't heard back yet.

I, too, use .PNG, but have been very disappointed with resulting alpha. I always get a shadow around the talent even when there is absolutely no visible shadow when keying directly in Vegas using New Blue chromakey. I also tried other chromakeyers such as cinecobs, and had the same problem using Logarith codec w/alpha.

I really wanted to save final rendering time by doing all the chromakey work as I shoot, then putting the rendered-&-keyed clip w/alpha on the time line, but have given up. I still do chromablur and saturate the green and do white balance, etc., and render that with PicVideo MJPG codec (or Cineform, without alpha), and put that clip on the TL. But the final compositing I do along with all other effects during final render so that I can get a cleaner key.

The only time when I rely upon .PNG alph now is when using Particle Illusion or other software outside of Vegas and have no other good option.

I, too, use .PNG, but have been very disappointed with resulting alpha. I always get a shadow around the talent even when there is absolutely no visible shadow when keying directly in Vegas using New Blue chromakey. I also tried other chromakeyers such as cinecobs, and had the same problem using Logarith codec w/alpha.

I am so glad I read your post. I have been getting the same black shadow but didn't realize that it was introduced when I saved it as an alpha layer encoded video. I am working on a project that has been giving me this problem and I thought it was in my keying. I didn't realize that I could avoid it by overlaying the keyed video directly against the background.

I've done a few experiments and it seems like it isn't just the Quicktime codec that has this problem. Is anyone successfully saving an alpha layer without introducing a bit of a black shadow around the edges? If so, what codec are you using?

If sticking to .AVI you must render to "Uncompressed." Using an .MOV you could render to the ANIMATION codec as well. I have never understood why Vegas doesn't let you render an alpha channel to codecs like lagarith, huffy uv, and cineform that support alpha channels. You can render an .AVI using these codecs in other programs that contain an alpha channel. Does anyone know why?