Only your current transponder.

You wouldn’t have to actually decode it, just receive it all and buffer everything after the last key frame. That eliminates waiting for the next key frame.

receiving it all _is_ the problem. nobody would pay the price for an RF front end with the bandwidth to digitize the entire OTA TV portion of the spectrum. they're spread from 54MHz to 806MHz. that's 752MHz of analog bandwidth. that's huge. (i'm not even sure you could buy that frontend for love or money. ok, maybe you take advantage of the gaps and just have 3-4 frontends. now there's a correspondingly large amount of PCB space taken up, more interference issues, increased defect rate, etc)

Essentially waiting for I-frames as the mini-GP noted it?