Bug#763736: Consider adding mpv-ffmpeg using ffmpeg instead of libav

[Fabian Greffrath]

Am Sonntag, den 09.11.2014, 20:13 +0600 schrieb Charles Malaheenee: 
> Sorry for stupid suggestion, but why not to try add alternative dependencies?
> Like as "libavcodec56 | libavcodec-ffmpeg56"?

Pretty sure the libavcodec libraries from libav and from ffmpeg do not
export the same symbols and are beyond that not ABI compatible anyway.

- Fabian