[FFmpeg-devel] [PATCH] Add alphaextract, alphamerge filters

[Steven Robertson]

Hi all,

I need to transmit a bunch of frames with a real-valued alpha channel
(not just a static mask) over a relatively slow link, and since the
recipient is on Windows, I'd like the relative simplicity of having
FFmpeg be the only tool that he needs to recover the content. A bit of
searching seems to indicate I'm not the first to want this, so I wrote
up a simple pair of filters to make this possible. From the patch
description:

"These filters are designed for storing and transmitting video sequences
with alpha using higher-efficiency codecs such as x264 which don't
natively support an alpha channel. 'alphaextract' takes an input stream
with an alpha channel and returns a video containing just the alpha
component as a grayscale value; 'alphamerge' takes an RGB or YUV stream
and adds an alpha channel recovered from a second grayscale stream."

Happy to address any review comments.

Thanks,
Steve
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