I don't understand why you need a special codec for Catalyst when the Prores family are perfectly adequate. You will be stuck with the 16 pixel multiple - nothing that can be done - its the way the codec decodes the data - see http://en.wikipedia.org/wiki/Macroblock.

What kind of computer are you trying to run 16 HD movies on? The new Mac Pro or Silver tower? There are very few machines that can run 16 HD movies at one time - certainly none of the silver towers could manage many more that 4!