PP will never recognize black as an alpha channel. You need to eliminate the black using the Luma key. So long as there's nothing else underneath, that now removed black will be encoded transparently as an alpha.
awesome... exactly what I was looking for
you'd think when spending an hour or more asking the question "how do you add an alpha channel to a video" this would think this would come up
having a weird issue now with it rendering a box in the lower right hand corner though... it bugs me that I don't know why it's there... but i'll just crop it out
again... thank you!
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FYI: Most After Effects users will reach for Red Giant Unmult (formerly Knoll Unmult) to knock out black: http://www.redgiantsoftware.com/products/all/knoll-unmult-free/
Luma key is not nearly as clean as Unmult. But you'll need AE.
Nice tip, Kevin. I just had to remove some black myself and it came out so-so. I'll give that plug-in a try.