Export frames to JPEG

[Andrew Baldwin]

Requested by DitOnTheLoose

Rationale: "Because when working with RAW I send stills to the set via telegram so people can reference to those when talking about reshooting something or just for archiving. With Jpeg I can use JPEGmini to reduce filesize drastically with just a click, which helps to send the images to mobile phones on set.

Of course it would be nice to be able to choose between multiple file formats.

the quickest and easiest way of course would be if I could disable the overlays with a key, that way I could at least use a simple screenshot."

[Andrew Baldwin]

1.2 allows FFMPEG param tweaking, including JPEG export