Added -j <concurrency_level> option which defaults to 4 when omitted.
Added -j <concurrency_level> option which defaults to 4 when omitted.

zimbatm/ffmpeg-static,kreldjarn/ffmpeg-decklink,kreldjarn/ffmpeg-decklink,kreldjarn/ffmpeg-decklink,kreldjarn/ffmpeg-static,kreldjarn/ffmpeg-static,zimbatm/ffmpeg-static,andreipoe/ffmpeg-static,kreldjarn/ffmpeg-static,michalliu/ffmpeg-static,kreldjarn/ffmpeg-decklink,andreipoe/ffmpeg-static,michalliu/ffmpeg-static,kreldjarn/ffmpeg-static