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How do I export video with an alpha channel?
I was given a number of video files in AVI format to convert into video files with an alpha channel. For each clip I was also given a corrosponding clip of a luma matte of the same footage.
I have read up in the forum and was able to key it using the track matte set to luma, but now I need to export the footage as video with an alpha channel. How do I do that in AE? What are my codec options? I’m working on a mac with quicktime files but the final deliverables are supposed to be AVI files. Can I deliver AVI files with alpha channels from AE 7 pro on a mac machine?
Thanks,
Michael Escher
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6 Replies
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Hi Michael,
It sounds like you’ve been given footage rendered as straight and need ro render it as premultiplied. Check out Aharon’s multimedia 101 podcast on the topic.
Simon
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Ok, here we go: send your footage to the render queue then, in the queue panel, click on the link for the Output Module. In the Output Module Settings dialogue, open the drop-down labelled Channels. Change from RGB to RGB + Alpha. Click Ok.
When you render the footage and bring it back into AE, you should find that toggling the transparancy button in the Comp panel reveals the transparancy info is still there (the transparent areas would take on the comp background colour if you hadn’t changed the channel settings before rendering).
If you still can’t see the transparency (if that makes sense: I don’t know how you can “see transparency”!), click on the footage in the project panel and hit command+F to bring up the interpret footage dialogue. Make sure AE is interpreting the footage as Premultiplied – Matted with Color (the colour in the color picker should match the bg colour of the original comp).
Hope this works for you,
Simon -
I’d just like to add that if you use the free lagarith codec, you can export the video with alpha and get a really great lossless compression
Graham
https://www.shiveringcactus.bravehost.com – Free FX for amateur films
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Thanks so much for your help on this. I really appreciate that you and others take the time to help us who are less than knowledgeable about these sorts of things.
God bless the cow.
Best.
Michael Escher
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Thanks a lot Simon, your tip save my life, I’ve searched for this tip for months. You couldn’t imagine that 2 years after your help, you can make someone happy, could you?
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or sometimes forget. needed to jog my memory
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