Where does Quicktime store its screen recordings?
As of OSX Sierra, it's here:

~/Library/Containers/com.apple.QuickTimePlayerX/Data/Library/Autosave Information




In there, there is a container/package/directory called Unsaved QuickTime Player Document.qtpxcomposition that contains a Screen Recording.mov file with the actual video. You can copy-paste that mov file wherever to save it permanently.



You can also double-click the Unsaved QuickTime Player Document file directly. That file opens in QuickTime, and allows you to save in a proper place. Note that sometimes QuickTime will fail to save a Screen Recording with the error "The operation could not be completed" (using File &gt; Export As might work, though), so copy-pasting is probably less prone to error.

My battery ran out when I was recording and found my file there.