Found the problem!
The AVSForums guide sets up a script for Avisynth to improve the quality of DVD playback through ffdshow, and this is being applied to HD content too, so the CPU can't cope.
I've tried turning off all filters bar ffdshow audio and CoreAVC in MPC, but when I check the filters in use, ffdshow video still shows up?
I can manually enable/disable it every time I change formats, but that'll be a right pain, any way to set my filters up so it uses the appropriate ones for the format being played?
The AVSForums guide sets up a script for Avisynth to improve the quality of DVD playback through ffdshow, and this is being applied to HD content too, so the CPU can't cope.
I've tried turning off all filters bar ffdshow audio and CoreAVC in MPC, but when I check the filters in use, ffdshow video still shows up?
I can manually enable/disable it every time I change formats, but that'll be a right pain, any way to set my filters up so it uses the appropriate ones for the format being played?