Alpha Channel + Smaller File Size + Quick Time

[Todd Kopriva]

Why are you concerned about the file size for intermediate files used in exchange between two post-production applications?

It make sense to be concerned about file size for final delivery or playback, but not so much for files used for input into another post-production application.

For such intermediate files, you want to keep as much data as possible.

If you’re using QuickTime, both the Animation codec and the PNG codec are good choices for keeping an alpha channel. Animation files are bigger, but they decode faster.

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Todd Kopriva, Adobe Systems Incorporated
After Effects quality engineering
After Effects team blog
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[Oliver Watson]

Todd, thanks for providing that insight. However, I am concerned about file size because inordinately large files will bog down even a tricked out Mac Pro. I’m struggling to keep a 13 minute video file with an alpha channel under 150 GB. That’s just unwieldy, even as an intermediate file. If anything it should be smaller than the video source file after pulling the colour key. The source file was only about 1 GB.

[Michael Szalapski]

[Oliver Watson] “If anything it should be smaller than the video source file after pulling the colour key.”

What? No. The exact opposite, in fact.

A file directly from most cameras is highly compressed. Take a DSLR for example. They all capture using a highly compressed h.264 codec.

If you put out any sort of intermediate file, it’s going to be significantly larger because you’re not outputting a highly compressed file.

AE does not simply add effects to a video file. It interprets a codec and then works on a fully uncompressed frame. What it renders afterwards is up to you, but the source(s) of any assets in AE are completely irrelevant to the size of the output.

– The Great Szalam
(The ‘Great’ stands for ‘Not So Great, in fact, Extremely Humble’)

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

[Oliver Watson]

Thanks, Michael. Yes, indeed. Nevertheless it makes no sense to me that AE cannot export the file with comparable compression. Adding an alpha channel should increase my overall data costs by 33%, and yet I can’t find a way to export the file without increasing its size by 10,000%. The math doesn’t make sense.

Not only that: I’m *removing* 80% of the RGB data in my frames by pulling this key. That far outweighs the cost of adding an alpha channel, and it seems strange that there is no compression scheme that takes advantage of this in the way that I imagine the ‘optimize stills’ setting takes advantage of static RGB values.