noname128 Ok, so at one point I had almost the exact same setup and headset as you, so here are my suggestions and maybe they will help:
1.) I assume you're talking about videos that you have downloaded, not just ones you are streaming? Which versions are you downloading, for example do you download the "Max 6/7/8k" version (for example it may be 8-15gb or something like that), or the full "Original" version that is much larger (usually 40+ gb)? Only ask since if it's the full "Original" version, it could just be that the very high bitrate is causing your 2070 to struggle a bit.
2.) Have you tried turning on "DirectShow" in the menu on the right hand side of DeoVR? I've found for quite a few different videos and some studios in particular this will help to make the video play smoothly as intended.
3.) I've also found with SteamVR and DeoVR that if I don't minimize the mirrored window of DeoVR on my actual desktop monitor, that it can cause some choppiness in my headset playback. So try minimizing the mirrored window on your desktop.
Hopefully one of these might help.