added video type ffmpeg

Hallo Doug,
I do struggle very long with xuggler and did not get far enough, so I created a new media type ffmpeg to interface directly to ffmpeg 2.2. I implemented opening and using ffmpeg videos and made the new video type usable with tracker. I would be happy if you considered including this video type in your repository.
This request consists of three parts, osp, video-engine, tracker.

Bye, Frank Schütte