Add ability to cancel or end frame capturin/encoding

Sometimes I decide mid-capture/encode of a video that I don't want to continue. It would be nice to have a "Cancel Video Save" button to cancel the video saving/uploading process so I don't have tl alt+f4 out of the app to stop it.

Also, sometimes the capturing goes for quite a while beyond what I'm interested in capturing, and I want to cap off the video early. It would be nice to have a "End Video Save" button available. Maybe there's a better name for that feature though.