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Netflix cuts 4K bitrate in half, promises same quality 4K video

15 Oct 2020 | Rasmus Larsen |

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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