Set autoexposure only once per orbital pass

[nrwahl2]

Russell reported:

The payloads to be transmitted from the satellite to the ground are short movies (currently 12 frames) constructed using ffmpeg from frames extracted from a usb webcam's v4l stream. The problem I encountered is that each movie restarts the usb webcam stream and resets the autoexposure, which takes a significant portion of the 12 frames to settle out. The obvious solution to this is to refactor the looping so that the usb-webcam stream is only started once per orbital pass, rather than once per mp4. A python program grabs the accumulated frames and manages the processes that create and transmit the movies.

[RussellSenior]

line 93 in current https://github.com/oresat/oresat-live-software/blob/master/camera/camera.py: subprocess.call(capture_command.split()) is inside the loop. This should get moved outside the loop, so it starts once, and the rest of the file processing/handling adjusted to grab the right number of frames for ffmpeg.