If I'm reading this right, the idea is that when the MPEG stream comes down the cable line, they will strip out any keyframes inside commercials. So instead of your keyframe interval being under a second, it would be several minutes long. I guess the assumption here is that DVRs implement fast-forward by scanning ahead to the next keyframe, rather than by decoding the whole stream and just not displaying some decoded frames, and the lack of keyframes at regular intervals would screw it up. But wouldn't this have exactly the opposite effect to what's intended? Wouldn't it make ffwd immediately skip the entire commercial block while scanning for the next keyframe, instead of showing the commercial in high speed as it does now?
US Patent 8,180,200.