4 ms·

Right, but there's a social/business reason why this is true. There are various things that could be done technically to fix this, for example, you could have

Right, but there's a social/business reason why this is true. There are various things that could be done technically to fix this, for example, you could have three decoders running simultaneously so you always had the adjacent channels buffered, you could send keyframes more often, or you could even use a totally different compression scheme that didn't use keyframes. The real reason problems like this aren't solved is that the organization does not allocate resources to fix them. The status quo has been deemed to be good enough and not leading to the loss of too many customers to the competition, so that's where it stands. This pervades all engineering -- everything just barely works, because once it barely works, for most things, it's good enough, and no more resources are deployed to make it better.

philwelch 6y ago
Realistically, it’s because it was considered an acceptable tradeoff for replacing 480i analog video with 1080p digital video.
- jfrunyon 6y ago
  By who? Many people wouldn't even be able to reliably tell the difference with common dpi's and viewing distances.
  - andrewstuart2 6y ago
    Between 1080p and 480i? Have you never watched old video/shows on an HDTV? The difference is stark.
    - AnIdiotOnTheNet 6y ago
      All the time, and unless the images are next to each other you don't really notice unless you're looking for it. Not because there isn't a big difference, but because you just don't really care that much unless it is called to your attention.
      - spanhandler 6y ago
        I've found pixel-count improvements stop mattering for me somewhere around DVD quality for a lot of content. I can tell the difference between that and 1080P, but stop caring once I'm actually watching the show/film. For the occasional really beautifully-shot film or some very detailed action movies, I guess I might care a little. 1080P versus 4K, I don't notice the difference at all unless I'm deliberately looking for it. And that's even with a 55" screen at a fairly close viewing distance. What does make a difference? Surround sound. I'd take 5.1 or up with DVD-quality picture over 4K with stereo any day, no hesitation.
  - formerly_proven 6y ago
    The difference between 576i50 (PAL equivalent, free version of the main private channels) and 720p50 (that's what German public service uses for "HD"; it's not actually 1080p, although they use a pretty high bitrate) is pretty stark, the difference between 576i and 1080p is even more obvious. Although TVs don't really have a neutral setting and try their best to mess every image up as much as they can.
  - philwelch 6y ago
    I remember a clear improvement in the legibility of things like onscreen scoreboards in sports broadcasts. In the NTSC era I would squint at the TV trying to figure out if the score was 16 or 18 for a football game, and for a basketball game you just had to keep track of it in your head since the scoreboard wasn’t even persisted onscreen. Other things, like telling different players apart, are also easier these days (you can even make out their facial features in a wide shot!)
  - projektfu 6y ago
    I remember seeing my first HD hockey game in a bar around 2000. Wow! I could actually see the puck.
VMG 6y ago
maybe it IS good enough
xwdv 6y ago
Hmm, those 2 seconds in between channel changes might be enough to insert a micro ad that could be preloaded in the background. That would appear instantaneously while your channel loads, it would feel a lot more responsive.
- jakeinspace 6y ago
  Just that thought makes me want to jump out the window.
cma 6y ago
Maybe it leads to less impulsive tv watching and aimless surfing and ends up being a benefit.
formerly_proven 6y ago
I think some boxes advertise that, but how much does it help? On an analog TV you could be switching channels at a rate of say 3-4 per second while still registering the channel logos and stopping on the right one (by going one back immediately). One receiver in either direction isn't going to keep the charade up. Some cleverness, like decoding adjacent channels, but if the user switches a channel down, have the "up" decoder jump to the 2nd channel down in anticipation of the user going another channel down etc., might help, but still. You can't feasibly emulate the channel agility (across ~800 channels on satellite) of an analog RF receiver in a digital system with a modulation that has a self-synchronisation interval of up to a few seconds. > you could send keyframes more often, or you could even use a totally different compression scheme that didn't use keyframes. GOP length / I-frame interval directly relates to bitrate. Longer GOPs generally result in a lower bitrate at similar quality; in DVDs or Blu-rays I believe the GOPs can be quite long (10+ seconds) to achieve optimum quality for the given storage space. Non-predictive video codecs are usually pretty poor quality for a reasonable bitrate (like a bunch of weird 90s / early 00s Internet video codecs), or near-losless quality but poor compression (because they're meant as an intermediate codec).
- cameldrv 6y ago
  Right but your assumption is that bandwidth efficiency is the only important thing. Why don't they use 10 second intervals if they're more efficient? My point is that there are many ways you could apply engineering, money, bandwidth, etc to reduce or eliminate the problem but they don't because they see it as good enough to not lose customers.
  - formerly_proven 6y ago
    Honestly it seems pretty obvious to me that the I-frame intervals that are typically used are the outcome of a balance between usability (having to wait until a clear picture can be viewed) and bandwidth as well as processing requirements. Bandwidth matters because spectrum is a finite commons. Digital TV required giving up bands that were in use for other things (e.g. wireless microphone systems and some ham bands) as it is, using even more bandwidth would have required even more spectrum. Other people have stakes in the spectrum for very good reasons and often much more important reasons than "I wanna watch TV". Even for satellite TV, which uses frequencies high enough that there is lots of bandwidth is limited, because using a lot of bandwidth would require new LNBs and multiswitches for all customers. > My point is that there are many ways you could apply engineering, money, bandwidth, etc to reduce or eliminate the problem but they don't because they see it as good enough to not lose customers. Can you name one for each category you bring up? Especially the "engineering" one would be interesting. Obviously dedicating an even huger chunk of spectrum to "I wanna watch TV" would make things easier, so that's not really interesting. And "let's just give each customer a TVoIP stream that can start immediately" is also a pretty obvious "money is no concern" (and also "we don't care about customer adoption costs") option.

philwelch 6y ago

Realistically, it’s because it was considered an acceptable tradeoff for replacing 480i analog video with 1080p digital video.

jfrunyon 6y ago
By who? Many people wouldn't even be able to reliably tell the difference with common dpi's and viewing distances.
- andrewstuart2 6y ago
  Between 1080p and 480i? Have you never watched old video/shows on an HDTV? The difference is stark.
  - AnIdiotOnTheNet 6y ago
    All the time, and unless the images are next to each other you don't really notice unless you're looking for it. Not because there isn't a big difference, but because you just don't really care that much unless it is called to your attention.
    - spanhandler 6y ago
      I've found pixel-count improvements stop mattering for me somewhere around DVD quality for a lot of content. I can tell the difference between that and 1080P, but stop caring once I'm actually watching the show/film. For the occasional really beautifully-shot film or some very detailed action movies, I guess I might care a little. 1080P versus 4K, I don't notice the difference at all unless I'm deliberately looking for it. And that's even with a 55" screen at a fairly close viewing distance. What does make a difference? Surround sound. I'd take 5.1 or up with DVD-quality picture over 4K with stereo any day, no hesitation.
- formerly_proven 6y ago
  The difference between 576i50 (PAL equivalent, free version of the main private channels) and 720p50 (that's what German public service uses for "HD"; it's not actually 1080p, although they use a pretty high bitrate) is pretty stark, the difference between 576i and 1080p is even more obvious. Although TVs don't really have a neutral setting and try their best to mess every image up as much as they can.
- philwelch 6y ago
  I remember a clear improvement in the legibility of things like onscreen scoreboards in sports broadcasts. In the NTSC era I would squint at the TV trying to figure out if the score was 16 or 18 for a football game, and for a basketball game you just had to keep track of it in your head since the scoreboard wasn’t even persisted onscreen. Other things, like telling different players apart, are also easier these days (you can even make out their facial features in a wide shot!)
- projektfu 6y ago
  I remember seeing my first HD hockey game in a bar around 2000. Wow! I could actually see the puck.

VMG 6y ago

maybe it IS good enough

xwdv 6y ago

Hmm, those 2 seconds in between channel changes might be enough to insert a micro ad that could be preloaded in the background. That would appear instantaneously while your channel loads, it would feel a lot more responsive.

jakeinspace 6y ago
Just that thought makes me want to jump out the window.

cma 6y ago

Maybe it leads to less impulsive tv watching and aimless surfing and ends up being a benefit.

formerly_proven 6y ago

I think some boxes advertise that, but how much does it help? On an analog TV you could be switching channels at a rate of say 3-4 per second while still registering the channel logos and stopping on the right one (by going one back immediately). One receiver in either direction isn't going to keep the charade up. Some cleverness, like decoding adjacent channels, but if the user switches a channel down, have the "up" decoder jump to the 2nd channel down in anticipation of the user going another channel down etc., might help, but still. You can't feasibly emulate the channel agility (across ~800 channels on satellite) of an analog RF receiver in a digital system with a modulation that has a self-synchronisation interval of up to a few seconds. > you could send keyframes more often, or you could even use a totally different compression scheme that didn't use keyframes. GOP length / I-frame interval directly relates to bitrate. Longer GOPs generally result in a lower bitrate at similar quality; in DVDs or Blu-rays I believe the GOPs can be quite long (10+ seconds) to achieve optimum quality for the given storage space. Non-predictive video codecs are usually pretty poor quality for a reasonable bitrate (like a bunch of weird 90s / early 00s Internet video codecs), or near-losless quality but poor compression (because they're meant as an intermediate codec).

cameldrv 6y ago
Right but your assumption is that bandwidth efficiency is the only important thing. Why don't they use 10 second intervals if they're more efficient? My point is that there are many ways you could apply engineering, money, bandwidth, etc to reduce or eliminate the problem but they don't because they see it as good enough to not lose customers.
- formerly_proven 6y ago
  Honestly it seems pretty obvious to me that the I-frame intervals that are typically used are the outcome of a balance between usability (having to wait until a clear picture can be viewed) and bandwidth as well as processing requirements. Bandwidth matters because spectrum is a finite commons. Digital TV required giving up bands that were in use for other things (e.g. wireless microphone systems and some ham bands) as it is, using even more bandwidth would have required even more spectrum. Other people have stakes in the spectrum for very good reasons and often much more important reasons than "I wanna watch TV". Even for satellite TV, which uses frequencies high enough that there is lots of bandwidth is limited, because using a lot of bandwidth would require new LNBs and multiswitches for all customers. > My point is that there are many ways you could apply engineering, money, bandwidth, etc to reduce or eliminate the problem but they don't because they see it as good enough to not lose customers. Can you name one for each category you bring up? Especially the "engineering" one would be interesting. Obviously dedicating an even huger chunk of spectrum to "I wanna watch TV" would make things easier, so that's not really interesting. And "let's just give each customer a TVoIP stream that can start immediately" is also a pretty obvious "money is no concern" (and also "we don't care about customer adoption costs") option.