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It's really too bad that they haven't rolled this out for 1080p too. Their 1080p video quality is god-awful compared to Amazon. They may even have made it worse

It's really too bad that they haven't rolled this out for 1080p too. Their 1080p video quality is god-awful compared to Amazon. They may even have made it worse: from the "ladder" comparisons, it looks like they jump to higher resolutions at lower average bitrates now, so if you're stuck at 1080p you're going to be getting worse quality after these changes than before. Also, something that's kind of weird about all this is that encoders (x264, x265, etc) already have their own rate control algorithms that decide on a frame or scene basis how many bits to use. Netflix taking an approach like this is equivalent to claiming that they're capable of doing a better job than these codecs in an automated way - so why not just contribute the code needed to achieve these improvements back to the projects they're using? Last, it's very weird to select individual frames from an encode and not a selection of frames. The comparisons purport to show that the lower bitrate encode is better than the higher bitrate encode, but in fact (if I understand how they're using rate control correctly) what they are showing is a single frame in the lower bitrate encode that uses more bits than the same frame in the higher bitrate encode. So it's arguably not a fair comparison. And even with that, depending on how sensitive you are to artifacts, some of the "optimized ladder" encodes still look worse. Edit: here is an example of what I mean when I said that they may have made the quality at 1080p worse. If what you end up watching is the highest bitrate 1080p available, you would get higher quality on the old latter than on the newer one. https://i.imgur.com/rzPR7Sh.jpg https://i.imgur.com/rzPR7Sh.jpg Actually, on some of the examples, even 720p on the older ladder is better than 1080p on the newer one!

crazygringo 6y ago
> It's really too bad that they haven't rolled this out for 1080p too Maybe they will? But it matters most for 4K performance, so that's where they started? > encoders (x264, x265, etc) already have their own rate control algorithms But they simply operate on a stream without taking future frames into account. This does a first entire pass on the film holistically to determine where keyframes should go and settings per-shot. It can't be backported to codecs because they work linearly. > And even with that, depending on how sensitive you are to artifacts, some of the "optimized ladder" encodes still look worse. The artifacts look worse only because it's zoomed in so crazy far. On a cinema screen, the additional sharpness will be clear, the artifacts not so much.
- bscphil 6y ago
  > This does a first entire pass on the film holistically to determine where keyframes should go and settings per-shot. It can't be backported to codecs because they work linearly. Given that x264 already has a 2 pass mode, I don't see why that is necessarily the case. Even CRF mode uses mbtree by default, which is a pretty complicated rate control algorithm. x264 also has pretty intelligent keyframe determination, I almost always see I frames on scene transitions. > On a cinema screen, the additional sharpness will be clear, the artifacts not so much. I think it's probably the other way around. The closer you are to a screen, the more likely you are to notice increased resolution. But if there are large patches of the image full of artifacts, you'll be likely to see that even far away.
  - zbobet2012 6y ago
    > Given that x264 already has a 2 pass mode, I don't see why that is necessarily the case. Even CRF mode uses mbtree by default, which is a pretty complicated rate control algorithm. x264 also has pretty intelligent keyframe determination, I almost always see I frames on scene transitions. x264 will not align keyframes across resolutions and encodes. In addition the pershot encodes optimize more than just idr frame placement. They also optimize other encoder parameters such as aq. > I think it's probably the other way around. The closer you are to a screen, the more likely you are to notice increased resolution. But if there are large patches of the image full of artifacts, you'll be likely to see that even far away. That isn't how this works. It's not a strict tradeoff between more artifacts and less sharpness by changing resolution. Downscaling -> Upscaling is simply another form of lossy compression. It may look better or worse than using those bits in another spot.
    - bscphil 6y ago
      > x264 will not align keyframes across resolutions and encodes. In addition the pershot encodes optimize more than just idr frame placement. They also optimize other encoder parameters such as aq. Sure, that's true. (Though I don't know why it matters that keyframes aren't aligned.) But at the end of the day the point is that Netflix has a better rate control algorithm, and this could be built into x264, even if it might require a significant amount of work. (Which I'm sure the x264 developers would be willing to do for a substantial quality improvement.) > That isn't how this works. It's not a strict tradeoff between more artifacts and less sharpness by changing resolution. Of course it's not a strict tradeoff. It's a loose one. And yes, it may look better or worse. That's really my only point in that section of the comment: that bumping up the resolution earlier in the ladder as they're doing is not a pure win, and it may look worse to some people depending on their viewing conditions.
zbobet2012 6y ago
> They may even have made it worse: from the "ladder" comparisons, it looks like they jump to higher resolutions at lower average bitrates now, so if you're stuck at 1080p you're going to be getting worse quality after these changes than before. No they have not made it worse. 1080p encoded at lower bitrate can look better than 720p at a higher bitrate. Or vice versa. Even to the trained eye. It depends on the scene dynamics.* In the ladders they posted (called a RD chart) we can clearly see they have made a better selection of the resolution to encode at a given target bitrate increase the video quality. They have posted the BD rates for this stuff, the gains are substantial (30% or more visual quality at the same bitrate). > Also, something that's kind of weird about all this is that encoders (x264, x265, etc) already have their own rate control algorithms that decide on a frame or scene basis how many bits to use. Netflix taking an approach like this is equivalent to claiming that they're capable of doing a better job than these codecs in an automated way - so why not just contribute the code needed to achieve these improvements back to the projects they're using? Because they've built a split and stitch encoder on top of the codecs. That means the code is built around x264, not into it. > Last, it's very weird to select individual frames from an encode and not a selection of frames. The comparisons purport to show that the lower bitrate encode is better than the higher bitrate encode, but in fact (if I understand how they're using rate control correctly) what they are showing is a single frame in the lower bitrate encode that uses more bits than the same frame in the higher bitrate encode. So it's arguably not a fair comparison. And even with that, depending on how sensitive you are to artifacts, some of the "optimized ladder" encodes still look worse. This is extremely true. * High action scenes tend to benefit from lower resolution with more bits spent on inter compression while slower scenes benefit from tighter intra compression.
- bscphil 6y ago
  > No they have not made it worse. 1080p encoded at lower bitrate can look better than 720p at a higher bitrate. Or vice versa. Even to the trained eye. It depends on the scene dynamics.* Well, of course that's correct. Take 1080p encoded at 100 Mbps and 720 encoded at 300 Mbps, I guarantee you that 1080p wins every time. :-) > In the ladders they posted (called a RD chart) we can clearly see they have made a better selection of the resolution to encode at a given target bitrate increase the video quality. I understand how an RD chart works, but I disagree with your conclusions. Reread my original post carefully - my point is that if you're stuck with 1080p as the maximum resolution, than the quality you can get with the revised ladder is strictly worse, because Netflix will want to jump up to UHD resolutions, but your device won't support it. (And even assuming that the UHD will be better based on this chart is kind of a leap, because it depends on what artifacts you're most sensitive to. Objective metrics ≠ subjective experience. In several of their comparisons, I prefer the lower res version because the new one is simply too artifacted.) > Because they've built a split and stitch encoder on top of the codecs. That means the code is built around x264, not into it. I understand the technical difference, but I'm still not convinced. Fundamentally what you get at the end of the day is a single continuous h.264 stream. The quantizer is chosen based on some rate control algorithm, and IPB frame choices are made by another algorithm. Netflix's improvement amounts to having a better rate control, that understands scene differences and uses lower quantizers on more complex scenes. There's fundamentally no reason why you couldn't add such a rate control algorithm to x264. It might require using a 2-pass mode, but it could be done.
zerocrates 6y ago
This post is more or less all about them extending things they already do for lower resolutions to 4K. And the graph you posted isn't quite showing what you're saying it is: these show the "4K" curves. When you're on a 1080-max device but have a strong connection, there are higher-bitrate 1080 streams available; they're just not on this chart because that's not what it's showing. In other words, what the curves are showing is just that they're switching to higher resolutions at lower bitrates than before, when your device supports them. Really the way to read it would be drawing lines vertically: given a fixed bandwidth, the "optimized" encode is always giving higher quality and often higher resolution.
causality0 6y ago
It's gotten so I use my Netflix subscription as a catalog more than a streaming service. If I find I really like something I pirate a higher-quality version of it.

crazygringo 6y ago

> It's really too bad that they haven't rolled this out for 1080p too Maybe they will? But it matters most for 4K performance, so that's where they started? > encoders (x264, x265, etc) already have their own rate control algorithms But they simply operate on a stream without taking future frames into account. This does a first entire pass on the film holistically to determine where keyframes should go and settings per-shot. It can't be backported to codecs because they work linearly. > And even with that, depending on how sensitive you are to artifacts, some of the "optimized ladder" encodes still look worse. The artifacts look worse only because it's zoomed in so crazy far. On a cinema screen, the additional sharpness will be clear, the artifacts not so much.

bscphil 6y ago
> This does a first entire pass on the film holistically to determine where keyframes should go and settings per-shot. It can't be backported to codecs because they work linearly. Given that x264 already has a 2 pass mode, I don't see why that is necessarily the case. Even CRF mode uses mbtree by default, which is a pretty complicated rate control algorithm. x264 also has pretty intelligent keyframe determination, I almost always see I frames on scene transitions. > On a cinema screen, the additional sharpness will be clear, the artifacts not so much. I think it's probably the other way around. The closer you are to a screen, the more likely you are to notice increased resolution. But if there are large patches of the image full of artifacts, you'll be likely to see that even far away.
- zbobet2012 6y ago
  > Given that x264 already has a 2 pass mode, I don't see why that is necessarily the case. Even CRF mode uses mbtree by default, which is a pretty complicated rate control algorithm. x264 also has pretty intelligent keyframe determination, I almost always see I frames on scene transitions. x264 will not align keyframes across resolutions and encodes. In addition the pershot encodes optimize more than just idr frame placement. They also optimize other encoder parameters such as aq. > I think it's probably the other way around. The closer you are to a screen, the more likely you are to notice increased resolution. But if there are large patches of the image full of artifacts, you'll be likely to see that even far away. That isn't how this works. It's not a strict tradeoff between more artifacts and less sharpness by changing resolution. Downscaling -> Upscaling is simply another form of lossy compression. It may look better or worse than using those bits in another spot.
  - bscphil 6y ago
    > x264 will not align keyframes across resolutions and encodes. In addition the pershot encodes optimize more than just idr frame placement. They also optimize other encoder parameters such as aq. Sure, that's true. (Though I don't know why it matters that keyframes aren't aligned.) But at the end of the day the point is that Netflix has a better rate control algorithm, and this could be built into x264, even if it might require a significant amount of work. (Which I'm sure the x264 developers would be willing to do for a substantial quality improvement.) > That isn't how this works. It's not a strict tradeoff between more artifacts and less sharpness by changing resolution. Of course it's not a strict tradeoff. It's a loose one. And yes, it may look better or worse. That's really my only point in that section of the comment: that bumping up the resolution earlier in the ladder as they're doing is not a pure win, and it may look worse to some people depending on their viewing conditions.

zbobet2012 6y ago

> They may even have made it worse: from the "ladder" comparisons, it looks like they jump to higher resolutions at lower average bitrates now, so if you're stuck at 1080p you're going to be getting worse quality after these changes than before. No they have not made it worse. 1080p encoded at lower bitrate can look better than 720p at a higher bitrate. Or vice versa. Even to the trained eye. It depends on the scene dynamics.* In the ladders they posted (called a RD chart) we can clearly see they have made a better selection of the resolution to encode at a given target bitrate increase the video quality. They have posted the BD rates for this stuff, the gains are substantial (30% or more visual quality at the same bitrate). > Also, something that's kind of weird about all this is that encoders (x264, x265, etc) already have their own rate control algorithms that decide on a frame or scene basis how many bits to use. Netflix taking an approach like this is equivalent to claiming that they're capable of doing a better job than these codecs in an automated way - so why not just contribute the code needed to achieve these improvements back to the projects they're using? Because they've built a split and stitch encoder on top of the codecs. That means the code is built around x264, not into it. > Last, it's very weird to select individual frames from an encode and not a selection of frames. The comparisons purport to show that the lower bitrate encode is better than the higher bitrate encode, but in fact (if I understand how they're using rate control correctly) what they are showing is a single frame in the lower bitrate encode that uses more bits than the same frame in the higher bitrate encode. So it's arguably not a fair comparison. And even with that, depending on how sensitive you are to artifacts, some of the "optimized ladder" encodes still look worse. This is extremely true. * High action scenes tend to benefit from lower resolution with more bits spent on inter compression while slower scenes benefit from tighter intra compression.

bscphil 6y ago
> No they have not made it worse. 1080p encoded at lower bitrate can look better than 720p at a higher bitrate. Or vice versa. Even to the trained eye. It depends on the scene dynamics.* Well, of course that's correct. Take 1080p encoded at 100 Mbps and 720 encoded at 300 Mbps, I guarantee you that 1080p wins every time. :-) > In the ladders they posted (called a RD chart) we can clearly see they have made a better selection of the resolution to encode at a given target bitrate increase the video quality. I understand how an RD chart works, but I disagree with your conclusions. Reread my original post carefully - my point is that if you're stuck with 1080p as the maximum resolution, than the quality you can get with the revised ladder is strictly worse, because Netflix will want to jump up to UHD resolutions, but your device won't support it. (And even assuming that the UHD will be better based on this chart is kind of a leap, because it depends on what artifacts you're most sensitive to. Objective metrics ≠ subjective experience. In several of their comparisons, I prefer the lower res version because the new one is simply too artifacted.) > Because they've built a split and stitch encoder on top of the codecs. That means the code is built around x264, not into it. I understand the technical difference, but I'm still not convinced. Fundamentally what you get at the end of the day is a single continuous h.264 stream. The quantizer is chosen based on some rate control algorithm, and IPB frame choices are made by another algorithm. Netflix's improvement amounts to having a better rate control, that understands scene differences and uses lower quantizers on more complex scenes. There's fundamentally no reason why you couldn't add such a rate control algorithm to x264. It might require using a 2-pass mode, but it could be done.

zerocrates 6y ago

This post is more or less all about them extending things they already do for lower resolutions to 4K. And the graph you posted isn't quite showing what you're saying it is: these show the "4K" curves. When you're on a 1080-max device but have a strong connection, there are higher-bitrate 1080 streams available; they're just not on this chart because that's not what it's showing. In other words, what the curves are showing is just that they're switching to higher resolutions at lower bitrates than before, when your device supports them. Really the way to read it would be drawing lines vertically: given a fixed bandwidth, the "optimized" encode is always giving higher quality and often higher resolution.

causality0 6y ago

It's gotten so I use my Netflix subscription as a catalog more than a streaming service. If I find I really like something I pirate a higher-quality version of it.