errors in the streamdaq process methods are maddeningly hard to debug

[sneakers-the-rat]

if one of the internal methods like _buffer_to_frame throws, then it shows up only when we try and close the video writer and find it has no ffmpeg process, which is an extremely ineffective traceback.

these methods should be split up, but seriously maybe even before that we should add proper error handling that propagates errors up into the main proc.