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?"
"Assuming the bitrates are the same, 48fps will require 80% of the bandwidth needed to handle 60."
Not exactly - while your 80% approximation is true for uncompressed footage, h.264 encoded video and essentially every modern day video compression schema will inherit data from the frame(s) before it. The higher the framerate, the less (generally speaking) the images will change between frames - leading to a reduction in data per frame.
As seen here, the 48fps video 94% of the size of the 60 fps video. Granted, this is a singular example, but at least it supports the concepts that I described above.
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.
Very interesting. Thanks for the detail. I guess the fixed GOP structure must be limited to HDV (MPEG-4). That flexibility is pretty awesome.
For what it's worth, I suspect what you describe (720p60 @ 6Mbps) is more than fine for most people. In other words, Cameron's idea that people will be going to theaters because of magical picture quality seems like wishful thinking. I suspect people go to theaters because they like going to theaters. It's social. It's big. It's immersive and (relatively) distraction-free - all part of a fun night out.
Are they going to go home to 720p60 @ 6Mbps and think 'gah!'. Unlikely.
> "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."
I'm sorry, but it needs to be stated: the above isn't true and the calculations have nothing to do with reality. H.264 supports pretty much any GOP structure and you don't get from frames to final bitrate by dividing frame rates by GOP size.
Accepting that I was mistaken about the rigidity of h.264 (a possibility I acknowledged up front), and assuming that you DID establish a GOP structure of 6 frames (at a constant bit rate) shooting for one minute at 48 fps would produce 80% of the data generated by shooting at 60fps.
Indeed, this ratio would be true if you used no compression at all. The point was that in a fixed GOP scheme (again, at a constant bitrate), the difference in FILE SIZE would increase with the difference in frame rate, so the idea that file sizes for 60 fps material would only be marginally larger than those for 48 fps seemed mistaken.
My only mistake was in assuming that the GOP is fixed in h.264. I agree that "you don't get from frames to final bitrate by dividing frame rates by GOP size." But then again, I never said you did.
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?"