Is there a visual quality difference between CoreAVC and MPC-HCs H.264 codec?
They both can use GPU hardware acceleration, so the 30% faster that their website claims doesn't really mean much to me, so I'm wondering if there is any difference in the visual quality that would make it worth the money to buy it.
That is not exactly true. MPC-HC using DXVA (ATI/nvidia/intel/s3 chrome) and Core AVC can only use CUDA (nVidia only).
Czech Republic