Can't seem to change 60fps .mp4 to 90fps for VR

I have some 3d movies in .mp4 file format and can't seem to use a custom 90fps for max smoothness in the rift. I'm using MaxVR so I can toggle to see the fps of the video and with these files they seem to stay at 60fps even though svp seems to be running and loading my system there is no change in fps output. With my .mkv files it seems to convert to 90fps just fine so I was wondering if anyone knew what might be the issue here and how to possibly fix it.

MaxVR uses LAV filters if that makes any difference to how .mp4 files would play with svp.

Any response would be welcome and appreciated.

Thanks