Screencastify has the ability to record a tab or the entire desktop. The Record Desktop feature works cross-platform: Windows, Mac or ChromeOS. It can also record in various resolutions and with two different audio input configurations: system audio or microphone.
When the screencast is finished, it can be renamed and stored within the extension popup window until you download it (as a .webm file), upload it to YouTube or delete it. Best part of all is that it's lightning quick.
Now students w/ Chromebooks can quickly capture, narrate and share their learning with you, the teacher!
Check out my screencast below and see for yourself!