Hardware accelerated FFmpeg build

[tgerring]

Added additional switches to configure FFmpeg build for GPU-accelerated x264.

Original build instructions appear to be taken from http://www.jeffreythompson.org/blog/2014/11/13/installing-ffmpeg-for-raspberry-pi/

A newer setup is at https://www.reddit.com/r/raspberry_pi/comments/5677qw/hardware_accelerated_x264_encoding_with_ffmpeg/

[guysoft]

Ok, this might break support for armbian devices. But I am willing to merge that until there is call for armbian support.

[guysoft]

@tgerring Also if you are writing any distro it would be great to share and document here 🙂

[tgerring]

Yes, amazing thank you! I have been thinking about putting together builds for Homebridge, hence the attractiveness of FFmpeg already being being "modularized".

As for Armbian, I wasn't aware of, but if architecture/model detection is needed for other OS, it shouldn't be too difficult to do a conditional based on a grep of uname -a or similar if someone with it installed is able to report it :)

[guysoft]

Yes, but currently I don't know of any other project depending on it.
@kamomil at the time did https://github.com/kamomil/VlcOS . But its not maintained. So you get priority.