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Notice he's leaning towards 48p as opposed to 60p, which is an already standardized framerate that your modern TV likely supports. I do not think that is an ac

by jwr 16y ago

Notice he's leaning towards 48p as opposed to 60p, which is an already standardized framerate that your modern TV likely supports. I do not think that is an accident. After all, once we all buy our new 3D TVs, something will have to happen for people to buy new TVs again in 3-4 years. And before you mention bandwidth considerations, I do not have actual data, but I suspect that when using H.264 High Profile, the difference in bandwidth between 48fps and 60fps won't be that large. There is a limit to how much you can change visually in a single second: human perception.

bpeebles 16y ago
48 divides evenly into 240, so in theory a 240Hz TV could take a 48Hz signal and display it without any pulldowns, while 120Hz is 2.5 times 48, so it needs to do some work to create extra frames. (And really, that's the main advantage, currently, of 120Hz and 240Hz: 24, 30, and 60 (the primary American frame rates) all divide evenly into them, unlike 24 into 60).
- alexqgb 16y ago
  Seems like you wouldn't count on the TV to do this work. Instead, you'd shoot at 48, then convert to 60 before delivery, in the same way that TV shows shot on film and edited at 24p subsequently convert to 25 for PAL markets and 29.97 for NTSC.
  - bpeebles 16y ago
    I would rather count on the media player (Blu-ray player or whatever) or TV to do it than in the source. Think of it this way: in NTSC, DVDs were either had hard 3:2 pull down for 24Hz to the 29.97Hz to show on the interlaced CRTs of the time. But now that we have TVs that can show 24Hz, if you play those DVDs they still have the interpolated frame artifacts. While if you left it up to software pulldown in the DVD player (which they basically all had, since I believe it was part of the standard), they can now be shown at the proper frame rate without interpolation. Most theatrical DVDs released after the early 2000s were 24Hz, as far as I know and depended on the DVD player to convert to NTSC. So now in modern players, they're outputted at 24Hz for 120Hz and 240Hz TVs. The only downside is if you get crappy TVs and/or Bluray players that do horrible pulldown, I guess. But I've gotten hardpulled down DVDs that look horrible as well (I'm looking at you, BBC).
  - jwr 16y ago
    Problem is, while you can devise ways of converting 24p to interlaced 29.97, getting from 48 progressive frames to 60 progressive frames isn't obvious to me at all. You'd have to add a frame every 4 frames. This would likely ruin the whole large framerate experience.
    - deleted 16y ago
      [deleted]
alexqgb 16y ago
Assuming the bitrates are the same, 48fps will require 80% of the bandwidth needed to handle 60. To the best of my knowledge, H.264 only supports two GOP structures (short = 6 frames / long = 15 frames), both of which operate independently from the playback speed. In other words, a short GOP setting produces 8 blocks per second running at 48, and 10 per second running at 60. Assuming a constant bitrate (I know, I know), the throughput of the entire system needs to increase by an additional 20% to handle 60. And that's where things fall apart. Consider the iTunes store, where I believe HD rentals top out at 720p. Or most HD broadcasters, who skew away from the 19.39 Mbps ceiling on the ATSC MPEG-2 spec in favor of programs encoded at 13.something Mbps (the legal floor) thereby allowing an SD channel encoded at ~6Mbps to be delivered in parallel. Does this exercise in bandwidth maximization impact the quality of the HD component? You bet. Do the networks care? If an additional SD means they can dramatically increase the number of ads served, then no, absolutely not. So regardless of how great the acquisition setup, and how awesome the playback system, there's always the network in between them to consider. And with providers moving toward bandwidth caps, I see picture quality going down, not up. So, streaming 1080p60 H.264 encoded at (say) 7-9 Mbps? Choice, yes, but total fantasy for the time being. Of course, Cameron is talking about making theaters competitive, so maybe that's his point. Given that BluRay has effectively failed as a universal home standard, and that instant-availability is hugely favored over order-and-wait programs, image quality of filmed entertainment at home is now tied to network limits. The real question, then, is "are there enough cinephiles who actually care?"
- masuel 16y ago
  H264 has no such limitation regarding gop structure. The levels (3.0, 4.1 etc) define (slightly indirectly) the DPB (decode picture buffer) size. This is how many frames must be held in memory at one time. The gop itself is not limited. Furthermore the compression rate for high frame rate actually increases for live action as there has been less change between the frames and even taking a fixed framerate. There are compromises to be made and faster framerate with a fixed bitrate may not be great for all usages but I think that you are being very, and unduly, pessimistic here. From my experiences at 720p 60fps and a 6 Mbps stream (which we currently have deployed) and a nice encoder you are looking at a very nice picture.
nitrogen 16y ago
I believe there are already some TVs that accept 48Hz as an input frame rate over HDMI. This is the only way 48fps video will look right, unless we move to 240Hz (the LCM of 48 and 60). 120fps would give the same juddery results as playing 24fps on a 60Hz display, but going up to 180 might be good enough to make the judder invisible (I don't notice the judder of a 24fps stream on an 85Hz CRT, but do at 60Hz, for example).
tpz 16y ago
Since no one else responded with this: you're right, it is not an accident that he would be considering 48fps, the reason being that a good amount of 24fps film projection occurs at 48fps on equipment that double pumps each frame. Such equipment (and the related equipment and processes around it) would likely be easier to upgrade/retrofit to 48fps than to 60fps.

by jwr 16y ago

bpeebles 16y ago

48 divides evenly into 240, so in theory a 240Hz TV could take a 48Hz signal and display it without any pulldowns, while 120Hz is 2.5 times 48, so it needs to do some work to create extra frames. (And really, that's the main advantage, currently, of 120Hz and 240Hz: 24, 30, and 60 (the primary American frame rates) all divide evenly into them, unlike 24 into 60).

alexqgb 16y ago
Seems like you wouldn't count on the TV to do this work. Instead, you'd shoot at 48, then convert to 60 before delivery, in the same way that TV shows shot on film and edited at 24p subsequently convert to 25 for PAL markets and 29.97 for NTSC.
- bpeebles 16y ago
  I would rather count on the media player (Blu-ray player or whatever) or TV to do it than in the source. Think of it this way: in NTSC, DVDs were either had hard 3:2 pull down for 24Hz to the 29.97Hz to show on the interlaced CRTs of the time. But now that we have TVs that can show 24Hz, if you play those DVDs they still have the interpolated frame artifacts. While if you left it up to software pulldown in the DVD player (which they basically all had, since I believe it was part of the standard), they can now be shown at the proper frame rate without interpolation. Most theatrical DVDs released after the early 2000s were 24Hz, as far as I know and depended on the DVD player to convert to NTSC. So now in modern players, they're outputted at 24Hz for 120Hz and 240Hz TVs. The only downside is if you get crappy TVs and/or Bluray players that do horrible pulldown, I guess. But I've gotten hardpulled down DVDs that look horrible as well (I'm looking at you, BBC).
- jwr 16y ago
  Problem is, while you can devise ways of converting 24p to interlaced 29.97, getting from 48 progressive frames to 60 progressive frames isn't obvious to me at all. You'd have to add a frame every 4 frames. This would likely ruin the whole large framerate experience.
  - deleted 16y ago
    [deleted]

alexqgb 16y ago

Assuming the bitrates are the same, 48fps will require 80% of the bandwidth needed to handle 60. To the best of my knowledge, H.264 only supports two GOP structures (short = 6 frames / long = 15 frames), both of which operate independently from the playback speed. In other words, a short GOP setting produces 8 blocks per second running at 48, and 10 per second running at 60. Assuming a constant bitrate (I know, I know), the throughput of the entire system needs to increase by an additional 20% to handle 60. And that's where things fall apart. Consider the iTunes store, where I believe HD rentals top out at 720p. Or most HD broadcasters, who skew away from the 19.39 Mbps ceiling on the ATSC MPEG-2 spec in favor of programs encoded at 13.something Mbps (the legal floor) thereby allowing an SD channel encoded at ~6Mbps to be delivered in parallel. Does this exercise in bandwidth maximization impact the quality of the HD component? You bet. Do the networks care? If an additional SD means they can dramatically increase the number of ads served, then no, absolutely not. So regardless of how great the acquisition setup, and how awesome the playback system, there's always the network in between them to consider. And with providers moving toward bandwidth caps, I see picture quality going down, not up. So, streaming 1080p60 H.264 encoded at (say) 7-9 Mbps? Choice, yes, but total fantasy for the time being. Of course, Cameron is talking about making theaters competitive, so maybe that's his point. Given that BluRay has effectively failed as a universal home standard, and that instant-availability is hugely favored over order-and-wait programs, image quality of filmed entertainment at home is now tied to network limits. The real question, then, is "are there enough cinephiles who actually care?"

masuel 16y ago
H264 has no such limitation regarding gop structure. The levels (3.0, 4.1 etc) define (slightly indirectly) the DPB (decode picture buffer) size. This is how many frames must be held in memory at one time. The gop itself is not limited. Furthermore the compression rate for high frame rate actually increases for live action as there has been less change between the frames and even taking a fixed framerate. There are compromises to be made and faster framerate with a fixed bitrate may not be great for all usages but I think that you are being very, and unduly, pessimistic here. From my experiences at 720p 60fps and a 6 Mbps stream (which we currently have deployed) and a nice encoder you are looking at a very nice picture.

nitrogen 16y ago

I believe there are already some TVs that accept 48Hz as an input frame rate over HDMI. This is the only way 48fps video will look right, unless we move to 240Hz (the LCM of 48 and 60). 120fps would give the same juddery results as playing 24fps on a 60Hz display, but going up to 180 might be good enough to make the judder invisible (I don't notice the judder of a 24fps stream on an 85Hz CRT, but do at 60Hz, for example).

tpz 16y ago

Since no one else responded with this: you're right, it is not an accident that he would be considering 48fps, the reason being that a good amount of 24fps film projection occurs at 48fps on equipment that double pumps each frame. Such equipment (and the related equipment and processes around it) would likely be easier to upgrade/retrofit to 48fps than to 60fps.