Something I've done, just with a cheap android phone... Set the phone on a stand and hit record. But not before I open up Reaper and hit record there, too. I have the keyboard hooked up to the computer such that Reaper gets the info (midi, it will do audio if I want it to) and records it.
Doing that, I have a good (and editable, yeah, I cheat a little, and can omit or correct a missed note) audio track and a video of the same that will match.
I add the video to Reaper, turn the sound from the phone's video off, and pair the two.
Perfect, no. But cheap, and using stuff I already have. With a little better lighting and some attention to visual detail, it could be considerably better. Heck, I could even add a second camera with another phone... If I ever decide to do something live, like a livestream, maybe I'd want to take things to a higher level. But for just getting a decent audio with a so-so video, it does work. Kinda depends on what you want and what you're trying to accomplish.