For 10.12.3 and before I've used AppleIntelFramebufferAzul. Worked fine for me, after apply it - never ever got any freeze from Safari.
But today I've decided to update to 10.12.4 and then right to 10.12.5. And it's freeze now on some sites WebGL disabled in Safari. Plugins disabled.
Ia anyone has the same problem? It's also freeze 100% every time on only these specific sites(I just give these links examples I've found so far, just by browsing web..): link 1or link 2
In Chrome all works without freezes.. but I need Safari, I like it.
I can confirm that installation of IntelGraphicsFixup 1.1.5 and Lilu 1.1.5 fixed Safari video freezes on 10.12.4 with both discrete (GTX750 Ti) and integrated (HD530) graphics cards enabled and used to drive two screens.