[bug#64732] [PATCH v3 1/2] gnu: Add python-ffmpeg-python.

[jgart]

Lars,

Should these be patched to refer to our ffmpeg?

https://github.com/kkroening/ffmpeg-python/blob/df129c7ba30aaa9ffffb81a48f53aa7253b0b4e6/ffmpeg/_run.py#L302

And a call to subprocess.check_call in the tests:

https://github.com/kkroening/ffmpeg-python/blob/df129c7ba30aaa9ffffb81a48f53aa7253b0b4e6/ffmpeg/tests/test_ffmpeg.py#L29

WDYT if we document our policy for patching executables. Currently, this 
practice is tribal knowledge that Guixers receive during patch review but we 
don't have it officially in writing anywhere (e.g. manual, cookbook, etc)

Ludo WDYT

all best,

jgart