How does cgms-a copy protection work?



As near as I can tell, it is a brodcast flag that digital equipment will pick up. what I don’t get is hbo uses it and they claim that you can convert to analog and then back to digital and it is still suposed to work. How exactlly does that work? Someone in the bargain basment is enquiring about the sima enhancer that is on sale and wondering if it will work. He is supoosedly recording in analog, and hbo claims to not use any analog protection. Is it possible that the cable box sees the flag and generates some sort of analog copy protection or something?
What kind of equipment would be sensitive to it, an analog capture card or a digital one?
Fyi yes I have tried googleing but have only found info on how it works with a digital signal. I don’t understand how it works with analog signals and why it would stop someone using an analog signal (to a stand alone dvd recorder or a capture device I am assuming).


Yes, the cable box generates Macrovision-type copy protection on the analog output when it sees the CGMS copy protection flag, which then prevents external DVRs and VCRs from recording it. You can only record it if you have an integrated PVR which includes the CGMS flag in the digital recording.


I asked this because another member was interested in a sima video enhancer for hbo problems (through analog). I am also quite interested in how it actually all works myself though. I would guess that the sima video enhancer would deal with it but who knows till someone tries (I have the enhancer but not hbo ore even cable right now). I’m more interested in it as it points to what the digital telivision future holds for us. I’m one of those that will be the last to hold out and stick to analog as all the restrictions on digital, hdtv, blue ray etc. sicken me, and anyway, I cannot aford it.
I also wonder if my exsisting and some old analog capture equipment will be subject to all this crap. I have an avertv stereo tuner/capture card, a pinacle capture/tuner card, both old (I think one didn’t even originally support win xp), I got a 20$ pos compusa capture card (good luck finding info on that one, it crashes either of my systems and is very much seems to be the driver causing the memory dump), and most resentlly, a pinacle studio av/dv with ver 9 of thier software (I never would have bought this but it was on clearance cheap and I had a store credit that had been burning a hole in my pocket for months and I could never find anything I wanted).
So basically , any chance with a bunch of old/cheap capture cards working into the digital tv age? Any hope that the sima will work for the other guy (he is looking at the ct-200, the same that that I have had for quite some time, and it works great for macrovision and all kinds of crap, when going from vhs to dvd).
Just wondering your general thoughts, not specifics.


Check the DVD Recorders forum over on (

There’s some interesting discussion of the different forms of copy protection on VHS tapes and DVDs, and how effective the different video correctors (like the various Sima models) are in dealing with the variations. Apparently more than one technique is used, and not all models can deal with all the techniques.


Thanks. I’ll look that over.