The cheapest would be to just use a constant neutral-grey i-frame whenever the channel flips, and update that until a real i-frame comes along, while playing the channel audio immediately. Ugly video for a second, but high-action scenes fill in faster. I'd bet that most people could identify an already-watched movie or series before an i-frame comes in, at least 80% of the time.

More expensive would be to cache incoming i-frames of channels adjacent to the viewed channel, and use the cached image instead of the grey frame. Looks like a digital channel dropping update frames during a thunderstorm for a second.

Prohibitively expensive (back then) would be to use multiple tuners that tune in to channels adjacent to the viewed channel, and then swap the active video and audio when the channel up or channel down buttons are pressed. Drop the channels that just exited the surfing window, and tune in to the ones that just entered it. Surfing speed limited by number of tuners.

Televisions still don't do this, even after more than a decade of digital broadcast, and multiple-tuner, multiple-output DVR boxes.

I've always suspected the reason it's slow is because you press the remote button, the DVR sends that to the provider, the provider has to verify that you can do what you are asking it to do, then a response comes, then the change can start.

I'm not sure who all is using it now but I used to work on the setup for Switched Digital Video. If nobody in your neighborhood was watching a certain channel, it would stop getting broadcast. That freed up bandwith for other things like internet. Once you would tune to a channel, a request would go to the head-end, it would quicky figure out if the channel is being broadcast in your area. If not, a request would go to the content delivery system to start feeding it to the QAM and then obtain what frequency the channel was on, and finally relay that back to the settop box which would tune and start the decoding process.

Rather impressive tech but again, this would add a bit more latency to that particular channel switching.