On a screen-recording github project here, I saw one line of code:
mCaptureScreenInput = [[NSClassFromString(@"QTCaptureScreenInput") alloc] init];
A google search for QTCaptureScreenInput reveals only two mentions on the web, that project and another one with an unused ivar of that type.
What is a QTCaptureScreenInput?
It's a private API. You can see here that QuickTime Player uses it to implement screen recording.