6 ms·

When working on digital settop boxes a decade or 2 ago, channel change latency was one of the toughest problems. Eventually we (collectively, the whole industry

When working on digital settop boxes a decade or 2 ago, channel change latency was one of the toughest problems. Eventually we (collectively, the whole industry) gave up and settled for 1 second as acceptable. Channel surfing quietly went away. When your i-frame only comes so often, there's not a whole lot you can do. Nowadays, that problem is solved by reducing actual live content to a strict minimum; everything else can be on-demand.

criddell 7y ago
These days they should be able to guess what 20 channels you might change to and start recording those in the background. 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.
- jaywalk 7y ago
  Nope, the STB has everything it needs to decrypt the channels you have access to. Tuning live TV channels happens 100% on the box. The only exception (a technology called Switched Digital Video) is just a way to save bandwidth on the cable, nothing to do with conditional access.
  - criddell 7y ago
    If I unplug my internet connection, my box won't let me do much at all. If I press pause or fast forward it just tells me the operation isn't authorized.
    - jaywalk 7y ago
      That's a weird system, certainly not the standard way of doing things on a traditional cable TV system.
      - criddell 7y ago
        I think it's pretty normal these days. The cable companies sell the data on what people watch, where the rewind, pause, fast forward, etc...
        jaywalk 7y ago
        No, it's absolutely not normal for a regular cable DVR to tie authorization for DVR functionality to an Internet connection.
        criddell 7y ago
        My last two have been like that. Try unplugging your internet connection then playing something you recorded earlier. If you have an AT&T or DirectTV DVR, it won't play.
- athenot 7y ago
  The slowness can also be because the channel you are trying to watch is not even there. 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.
  - Piskvorrr 7y ago
    And that's one of the reasons things seem worse: there are massive, clever efforts to provide an infinity of options, but they're not completely seamless. Compared to the do-one-thing-and-one-thing-only appliances of yesteryear, it necessarily looks bad, especially when looking through the memory's rose-tinted glasses.
logfromblammo 7y ago
Maybe there's not a lot you could have done while keeping the hardware cheap. I can think of a few ways to improve the user experience of channel surfing without waiting for an i-frame every time. 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.
Nextgrid 7y ago
Can't there be a dedicated channel or connection that's always tuned to that just broadcasts I frames from all channels, so that the box has all the latest frames for all channels and can start playing instantly when switching channels?

criddell 7y ago

These days they should be able to guess what 20 channels you might change to and start recording those in the background. 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.

jaywalk 7y ago
Nope, the STB has everything it needs to decrypt the channels you have access to. Tuning live TV channels happens 100% on the box. The only exception (a technology called Switched Digital Video) is just a way to save bandwidth on the cable, nothing to do with conditional access.
- criddell 7y ago
  If I unplug my internet connection, my box won't let me do much at all. If I press pause or fast forward it just tells me the operation isn't authorized.
  - jaywalk 7y ago
    That's a weird system, certainly not the standard way of doing things on a traditional cable TV system.
    - criddell 7y ago
      I think it's pretty normal these days. The cable companies sell the data on what people watch, where the rewind, pause, fast forward, etc...
      - jaywalk 7y ago
        No, it's absolutely not normal for a regular cable DVR to tie authorization for DVR functionality to an Internet connection.
        criddell 7y ago
        My last two have been like that. Try unplugging your internet connection then playing something you recorded earlier. If you have an AT&T or DirectTV DVR, it won't play.
athenot 7y ago
The slowness can also be because the channel you are trying to watch is not even there. 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.
- Piskvorrr 7y ago
  And that's one of the reasons things seem worse: there are massive, clever efforts to provide an infinity of options, but they're not completely seamless. Compared to the do-one-thing-and-one-thing-only appliances of yesteryear, it necessarily looks bad, especially when looking through the memory's rose-tinted glasses.

logfromblammo 7y ago

Maybe there's not a lot you could have done while keeping the hardware cheap. I can think of a few ways to improve the user experience of channel surfing without waiting for an i-frame every time. 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.

Nextgrid 7y ago

Can't there be a dedicated channel or connection that's always tuned to that just broadcasts I frames from all channels, so that the box has all the latest frames for all channels and can start playing instantly when switching channels?