Video2x, for example, extracts each frame to a folder before upscaling them and then compiling them back into a video. I can't find a folder anywhere for Hybrid that has a bunch of png images so I guess this isn't the case? Are they all just stored in ram? That's a lot of data ...
Never heard of Video2x.
Hybrid mainly works with Avisynth and Vapoursynth which don't process video by extracting each frame to the hdd.
Yes, during decoding and filtering frames are stored in RAM, but only a few so it's not really an issue.
Saving images on hdd is the odd behavior, no video processing tool I know would do that normally.
Cu Selur