Insider tip:
Ideally you want to make sure that your trainer can see your movements. Look for an angle to place your camera so they can see your whole body while exercising on the mat (and you can see them!). Placing the camera on the floor (if you have enough space) or higher up pointing it down (for smaller spaces), filming yourself from the side, will give the best result.
Of course during group classes it’s hard(er) to see everyone. If you are really keen on improving your posture with detailed feedback, I would highly recommend a 1-1 session.