Can't Increase Playback Speed on Video Files

[solrage]

I have some 4k UHD discs I've ripped to MKVs. After watching the films I like to listen to commentaries on 2x speed using PotPlayer (I've also tried MPC-BE), but with these MKV files I cannot. I've tried using Vidcoder/Handbrake to reencode to mp4/H.264 and but the problem persists. I've Googled the issue and while there are several suggestions, none of them have worked. I've tried:

-Using the --engage all_i_slices_are_key_frames in MKVMerge

-Using the --uhd-bd in Vidcoder/Handbrake

Any other suggestions? I don't care about quality as I will be deleting the file after listening to the commentary.

EDIT: After more experimentation, I discovered I CAN do 2x playback on VLC. While this can work there are some annoyances, like the fact that VLC isn't customizable and I have to hunt down the file in the folder structure. Anyone know why the VLC playback speed increase works but not on PotPlayer or MPC-BE?