Thomas,
Hangouts on air are the recorded versions of Google Hangouts,
they are streamed and recorded via Youtube. Screencasts, I thought,
also defaulted to being recorded.I know during my years of teaching, video was often preferred by students simply because even in step by step instruction, aka hand holding, there would be something glossed over, ignored or assumed known by students or the teacher. Video shows every keystroke, command and mouse movement
