record a mac output for a video

I need to do a series of iso (then multi cam) lecture videos

so i need to get a video recording of the mac mini output that is used for the presentations.
I am hoping to record via HDMI but am slightly worried about HDCP

I looked at the blackmagic video assist ( like a ninja) as a simple solution.

Normally i would just bung it through a vision mixer but can't.

anybody got a cheapish solution?

I did wonder about a games capture device?