MPlayerX is an alternative media player powered by ffmpeg and mplayer. MPlayer OS X ran OK, but it was slow. And also, the new technologies from Apple prevailed--such as Core Animation, Grand-Central Dispatch, even OpenCL--and pushed me to give them a try.
So I started without even knowing how to program under Mac, came to know Xcode, Objective-C 2.0, Cocoa, and the Core family. MPlayerX is still in such a primary stage, I will keep on enhancing it, and figure out how to do this and that.