Is It Possible To Digitize Into a Computer HDMI From a Cable DVR?

For professional reasons, I would like to be able to record into my Mac Pro a scene from a movie that has been recorded in my cable system’s DVR. So that I could then convert it to QuickTime and work with it within my computer’s software. I’ve tried a few things but haven’t been able to get the HDMI into my computer. Is this possible to do? Does HDMI use some kind of copyright protection system?
I’m using the latest iOS 6 10 on a Mac Pro late 2013.
Thanks, JR
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Joe Renzetti