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Netflix is reencoding all 4K, HDR and HFR titles in its catalog. The company claims to be able to deliver same quality 4K video at half the bitrate.

Netflix is reencoding 4K streams
While Apple TV+ has set new standards for video streaming quality with 4K streams exceeding 40 Mb/s bitrate at times, Netflix is moving in the other direction. The company is currently reencoding its 4K library with a focus on optimizing bitrate.

Netflix has been using per-title or per-shot encoding for a few years now, meaning that it takes the type of content or scene into consideration when encoding the content. These principles have been applied to SD/HD resolution and 8-bit video only but are now also being rolled out for 4K, HDR (High Dynamic Range) and HFR (High Frame Rate) streams, the company said.

Netflix claims that its new encoding approach can cut bitrates for 4K video in half without affecting picture quality.

- "Computing the Bjøntegaard Delta (BD) rate shows 50% gains on average over the fixed-bitrate ladder. Meaning, on average we need 50% less bitrate to achieve the same quality with the optimized ladder," the company said in a blog post. "For members with high-bandwidth connections we deliver the same great quality at half the bitrate on average. For members with constrained bandwidth we deliver higher quality at the same (or even lower) bitrate."

Other advantages of the new approach include "higher initial quality", "fewer quality drops while streaming", less rebuffering, and a reduction in "initial play delay by about 10%", according to the company.

One extreme example is "showing the new highest bitrate to be 1.8 Mbps ... for a 4K animation title episode" but Netflix noted that some scenes will also exceed 16 Mb/s bitrate, which used to be the maximum bitrate for 4K. In one example, an action scene hit 17.2 Mb/s.

- "Sometimes we ingest a title that would need more bits at the highest end of the quality spectrum — even higher than the 16 Mbps limit of the fixed-bitrate ladder. For example, a rock concert with fast-changing lighting effects and other details or a wildlife documentary with fast action and/or challenging spatial details."


Netflix 4K streaming
AN EXAMPLE OF NETLFIX'S OPTIMIZED 4K ENCODING. PICTURE: NETFLIX

Reports of reduced 4K quality
Not everyone is convinced. There are multiple reports on forums from subscribers who see a reduction in 4K streaming quality. Those complaints may become more widespread as Netflix releases more of its 4K reencodes over the coming weeks and months.

- "We have started re-encoding the 4K titles in our catalog to generate the optimized streams and we expect to complete in a couple of months. We continue to work on applying similar optimizations to our HDR streams," Netflix said in late August 2020.

To be clear, the latest initiatives are not related to Netflix's lowered streaming quality due to the coronavirus situation earlier this year. However, the influx of new users may have prompted Netflix to consider various optimizations.

Still, it is clear that Netflix is focusing mainly on reducing bandwidth rather than using the optimizations to deliver improved, less compressed 4K video quality.

- Source: Netflix
 

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their dolby atmos is not up to dolby standards
 

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If they were adopting AV1 or H.266, maybe they could cut bitrates that much and still maintain quality.

But it sounds like they're going to reencode with the same codecs?
 

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AV1/H.266 would require capable hardware to support it. VBR encoding with existing codecs doesn't. I can see this as being a win (same general quality, reduced bitrate, potentially improved quality in high-bitrate scenes) or loss (reduced quality to save bandwidth), all depending on the implementation.
 

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I'm old enough to remember when general business models strove to improve quality rather than the other way around.
 

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I'm old enough to remember when general business models strove to improve quality rather than the other way around.
Quality is subjective. I guarantee you most Netflix customers don't give a rodent's behind about picture or sound quality to the extent that this change will be noticed. They may care about avoiding hitting internet usage caps though.
 
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Discussion Starter #7
AV1/H.266 would require capable hardware to support it. VBR encoding with existing codecs doesn't. I can see this as being a win (same general quality, reduced bitrate, potentially improved quality in high-bitrate scenes) or loss (reduced quality to save bandwidth), all depending on the implementation.
So does this mean they could potentially increase bitrate in scenes that require them (like say with mass confetti) and decrease them in mostly static scenes?
 

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So does this mean they could potentially increase bitrate in scenes that require them (like say with mass confetti) and decrease them in mostly static scenes?
I think that's exactly what it means (the example they give is the rock concert rather than confetti, but the principle is the same). But what they are admitting is that today they encode everything at max and let the available bandwidth do the work. So shot-by-shot encoding won't make things better for such scenes, just keep it the same at best.

Having said that, I have to suspect that any complaints about decreased quality are highly likely to be confirmation bias or just the power of suggestion, since they are rolling this out slowly and there's no way to tell which shows/episodes have been re-encoded.

I did enjoy the terminology about "ingesting" titles -- the Netflix encoder is apparently gobbling up everything in sight.
 

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Having said that, I have to suspect that any complaints about decreased quality are highly likely to be confirmation bias or just the power of suggestion, since they are rolling this out slowly and there's no way to tell which shows/episodes have been re-encoded.
Also important to keep in mind is that Netflix tests everything before they implement it. So it's likely they've been streaming test titles months ahead of their blog post to make sure if any PQ issues crop up. And monitoring reactions from sharp eyed tech enthusiasts.
 
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