Here's my 2 cents. This does not apply to the out-of-the-box, "Show & Tell" kind of video where quality, performance and musicianship are unimportant.
A MUSIC VIDEO cannot be any better than its audio. Capturing your sound with nothing but the built-in video camera microphone is a bad idea - particularly if your camera is placed in a club or cafe where people are talking and/or guzzling beer and noisily stuffing their faces with fries.
With the theremin, given a choice, I'd rather see poor video with great audio, than poor audio with great video.
KEEP IT SHORT. Remember the immortal words of the late Clara Rockmore: LESS IS MORE. Leave your viewers wishing your three minute video was longer, rather than putting them to sleep with fifteen or twenty minutes of your glorious playing.
EDIT! EDIT! EDIT! There are so many theremin videos on YouTube where the first two or three minutes are all set-up, or images of an empty stage. This is often the case with concerts and festivals where a camera has been placed at the back of the hall and allowed to run for the entire event.
Why are you making a video?
If you're not sure exactly what it is you want to say with your performance, your audience won't know either. Bad theremin playing does not promote either the instrument or the career of the thereminist. I often wonder why people post videos where the remarks in their info box begin with, "I know my playing really stinks and the camera wasn't too steady but........".
If the person plays badly and doesn't know it, then it's not their fault. But if they play badly and know it, then what is their point?
It is a puzzlement!