Also leaving 0_8 branch, as it's compatible with older ffmpeg versions.
I'm planning that all expressions will be able to switch easily
between ffmpeg and libav (whatever default we choose, but I prefer libav).
Edited (twice) according to notes on the reverted b003138.
This reverts commit b0031380816d5b1f9767bc62a799083790e69a7e because
it breaks Nixpkgs evaluation with "error: attribute `cross.config'
missing".
http://hydra.nixos.org/build/5725600
Also leaving 0_8 branch, as it's compatible with older ffmpeg versions.
I'm planning that all expressions will be able to switch easily
between ffmpeg and libav (whatever default we choose, but I prefer libav).
