I would add that the native video, which comes out as mp4, also has sound. You cannot add your own mic into the video though. That can only only be done when you are casting to Facebook. You get a lot of BS when searching as to why mic does not work except for casting.
Have been doing audio work almost exclusively since July, and have figured out how to trick Oculus to record from mic in addition, at least if you bought the Oculus headphones wt mic accessory (I did). Here is how to do that for someone wanting to post videos with mic added.
I was making short voice recordings (on a desktop), and I wanted to play a piano key at the same time so the person could get close to that pitch, but not get the piano in the recording. Playing the piano key on the headphones did the trick, almost. You cannot hear yourself near as good with headphones, and makes it harder.
I fixed this by getting a 2nd mic stream:
// get second audio in, so can play it through headphones ( you can have more than one )
micStream = stream;
When doing the recording, I would just make a small audio graph, and it would get merged with the piano, without my code even knowing it. (The piano in your case represents any other sound your scene produces)
const audioInput = audioContext.createMediaStreamSource(micStream);
The device video recording process would not have a clue that this is coming from mic. You might get feedback if you use the std mic / speakers though. Solution might be use another headphone / mic combo you have, as long as the jack is the same.
Also, you basically have almost zero chances of generating a 3D video unless Oculus adds this as a feature.