Is the problem on your HTPC or your Workstation?
If it is on the PC as per your signature, it should be powerful enough. i.e. "Intel Core i5-4590 CPU, Haswell Gen2, LGA1150, 3.3GHz 6 DDR3/ 2x PCIE3.0 x16 16gb Ram Windows 10 64 bit Asus Z97-DELUXE ATX Motherboard Nvidia GForce gtx1080 Receiver Onkyo TX-NR925 TV LG LF6300 55" smart TV".
My old Workstation can play 50fps fine, although it does have an i7 processor, it is ten years old. i.e. Intel i7 960 3.20 GHz, Gigabyte GA-X58A-UD5 Rev. 1.0, Corsair CMD12GX3M6A1600C8 (6x2GB) DDR3, Sapphire HD5870 Vapor-X 1GB.
Play one of the videos, open the madVR Debug OSD display, and see if frames are being dropped, or queues are emptying, that the video is playing at 50Hz, etc. See image of what my Workstation example.