Choppy video output

Hi,

I tried to add some Harry's lap timer data to a gopro video and I am getting a very choppy output. It's as if it would be like 20 fps max sometimes. I'm using v 3.7.3 with win 10 up to date, up to date drivers for my 6900 xt.
I only ever used it once, in early may, but I don't remember it doing this. Any ideas? I already tried exporting both mp4 or wmv and it doesn't make a difference. The input video is fine of course (it's h.264 format, i recoded it from the original h.265 so i can add it to Racerender).

edit: uploaded a test here but i think it's pretty self explanatory...
https://youtu.be/YU3Q4-8XynE

That certainly does seem choppy... If the h.264 video plays back fine in VLC or something similar, then maybe double check the settings when rendering in RaceRender? Perhaps it has something like 50fps set instead of 60 or 24 instead of 30? I also recommend using maximum/best quality on the slider since better quality is preferable to shorter render times (at least to me).