Sorry, but OpenCL is not API for hardware H.264 decoding as we know it on other platforms. Yes, OpenCL allows you to run code on GPU, but that's where it ends. It is no match to DXVA in Windows or VA-API/VDPAU in Linux, which allows you using the silicon dedicated to decoding MPEG-2/4 ASP/4 AVC/VC-1. There is no equivalent to these APIs in OSX.