I ran into this question years back, and at the time began desperately searching for an answer as I was on the clock with a client.  Having worked with Avid at that point for many years I had never really attempted to export an alpha channel directly from Avid, since no client had really requested it, but I assumed that it was possible based on the docs that come with Avid and of course just plain common sense.

But then I discovered the fatal misconception that common sense and software don’t always go hand in hand.  Even if the documentation says it does.  So here are the facts people, and I’m gonna make this as clear as possible. 

If your reading this, you probably know what an alpha channel is but for the newbie’s I’ll make it real simple.  So first of all what is an alpha channel? 

An alpha channel is a portion of each pixel’s unused data that is reserved for transparency information.  Really, it is essentially a mask, it specifies how the pixels colors should be merged with another pixel when the two are overlaid.  Now back to issue at hand, the big question is can you export an alpha channel unmatted from Avid?

NO.  YOU CANNOT EXPORT A STRAIGHT UNMATTED ALPHA CHANNEL FROM AVID.  

There it is.  I know that the documentation may say differently but I think whoever wrote it was drinking the Jim Jones Koolaid at the time, or at least should have shortly there after because there is no codec, export option, or miracle that can provide your client or whomever with an unmatted alpha channel for them to import into whatever they are using and drop a background in.

It’s amazing how years later this is still an issue with Avid, despite constant complaining from it’s users and people who are desperately convinced that there is some way or form to do it.  There isn’t.  And Avid moderator ( via their website ) and customer support now admit that there is no way to do from within the Avid software.  The only solution is to bring the footage or sequence into a third party software ( such as AE ) and re-export the footage from there. 

So I just thought I would clear that little misnomer up since even today it is still a question on the minds of editors who run into this problem usually when they are on a deadline and begin to panic.  Until Avid fixes this, we’ll all just have to deal with it.