DirectX 12 is Windows 10 exclusive and that came out 1-2 years after 4th gen, so this would not be a feature Intel was advertising at the time.

I had a 4th gen processor (i5-4200) and it couldn't render video without lag until until the OS was upgraded to Windows 10 with DirectX 12, after which it was more than capable of handling video. DX12 probably added a few years to the life of my computer.