To create a screencast, you need a program (recordmydesktop, Kazam, are two I have used) that will record in video and audio anything you do or speak while screencasting.

A screencast is a video and audio record of how to do something, that would take a long time to explain by text files, still pictures and screenshots, etc. The adage: 'A picture is worth a thousand words' sums up how useful a screencast can be.

A screencast quickly summarizes what would otherwise take longer to explain. For example, we used a screencast to show how our library users can download free music (libraries are great for that)!

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yes its perfectly safe!

I dont know but go to screencast o matic.com and you should find it here