Apple ProRes 4444 Support

[pentool]

I'm not sure if this would be possible to add, but on the Mac "Apple ProRes 4444" can render out videos with transparency. Would be great to have a selectable output for this codec. Technically one could render a black background with a white track and use this as an alpha for video mask, but the ProRes 4444 option would be faster to do it :-) This way if the background map has opacity, it would also be a piece of cake to render it out in one fell swoop and just composite this over another video.