Netflix Expands AV1 Codec Streaming To Smart TVs
Netflix has begun streaming content encoded with the three-year-old high-efficiency codec AV1 from the Alliance of Open Media (AOMedia) on supporting smart TVs, expanding the range of devices beyond Android mobile products.
The world’s largest video streaming network announced the move in a blog on the company’s web site, Tuesday.
“AV1 is the first high-efficiency video codec format with a royalty-free license from Alliance of Open Media (AOMedia), made possible by wide-ranging industry commitment of expertise and resources,” the announcement said. “Netflix is proud to be a founding member of AOMedia and a key contributor to the development of AV1. The specification of AV1 was published in 2018. Since then, we have been working hard to bring AV1 streaming to Netflix members.”
Other AOMedia contributors and members include: Amazon, Apple, Facebook, Google, IBM, Intel, Microsoft and Mozilla.
In addition to Netflix, AV1 is also in limited use today by YouTube for the distribution of some 8K content streams, and YouTube’s parent Google reportedly plans to expand that use to other formats going forward.
AV1 is among a handful of emerging high-efficiency codecs competing as an alternative to the pervasive High Efficiency Video Codec (HEVC) codec that has been in widespread use since the launch of the first 4K UHD TVs and Ultra HD Blu-ray players. AV1 is positioned as both a claimed more efficient alternative to HEVC and a format with fewer IP patent pool licensing entanglements and royalty obligations, although there have been some recent IP claims and potential challenges to that stated royalty free status.
The alleged AV1 support requirement in streaming devices is also among a list of the reported disagreements between Google and Roku and is threatening the removal of the YouTube app from the Roku platform library next month. (Note that pre-existing installations of the app will continue to be supported). Among other reasons, the AV1 codec requires more powerful and expensive hardware processing than many Roku TVs and streaming devices can current support.
Netflix has not yet announced mandated requirements for AV1 support by third-party devices.
Netflix started streaming AV1 encded content to its Android Mobile App in February 2020. That launch “leveraged the open-source software decoder dav1d built by the VideoLAN, VLC, and FFmpeg communities and sponsored by AOMedia. We were very pleased to see that AV1 streaming improved members’ viewing experience, particularly under challenging network conditions,” the company said.
Netflix isn’t entirely abandoning users and devices with smart TVs that don’t currently support AV1. The streaming service has long supported multiple codecs for its users and transcodes content streams to ensure programs remain viewable on legacy devices.
“Netflix encodes content into multiple formats and selects the best format for a given streaming session by considering factors such as device capabilities and content selection,” the company assured customers.
But for those with supported devices, Netflix has identified a list of benefits including the following:
“Higher VMAF scores across the full spectrum of streaming sessions
• VMAF is a video quality metric developed and open-sourced by Netflix, and is highly correlated to visual quality. Being more efficient, AV1 delivers videos with improved visual quality at the same bitrate, and thus higher VMAF scores.
• The improvement is particularly significant among sessions that experience serious network congestion and the lowest visual quality. For these sessions, AV1 streaming improves quality by up to 10 VMAF without impacting the rebuffer rate.
More streaming at the highest resolution
• With higher compression efficiency, the bandwidth needed for streaming is reduced and thus it is easier for playback to reach the highest resolution for that session.
• For 4K eligible sessions, on average, the duration of 4K videos being streamed increased by about 5%.
Fewer noticeable drops in quality during playback
• We want our members to have brilliant playback experiences, and our players are designed to adapt to the changing network conditions. When the current condition cannot sustain the current video quality, our players can switch to a lower bitrate stream to reduce the chance of a playback interruption. Given AV1 consumes less bandwidth for any given quality level, our players are able to sustain the video quality for a longer period of time and do not need to switch to a lower bitrate stream as much as before.
• On some TVs, noticeable drops in quality were reduced by as much as 38%.
Reduced start play delay
• On some TVs, with the reduced bitrate, the player can reach the target buffer level sooner to start the playback.
• On average, we observed a 2% reduction in play delay with AV1 streaming.”
Explaining why AV1 support came to Android mobile devices prior to smart TVs, the company said: “AV1 playback on TV platforms relies on hardware solutions, which generally take longer to be deployed. Throughout 2020 the industry made impressive progress on AV1 hardware solutions. Semiconductor companies announced decoder SoCs for a range of consumer electronics applications. TV manufacturers released TVs ready for AV1 streaming. Netflix has also partnered with YouTube to develop an open-source solution for an AV1 decoder on game consoles that utilizes the additional power of GPUs.”
The company said that viewers without AV1 supporting smart TVs will be able to stream content with the codec streaming Netflix through connected PlayStation 4 Pro consoles.
Using AV1, Netflix said it will “always encode at the highest available source resolution and frame rate to preserve the artistic vision.
“All AV1 streams are encoded with 10 bit-depth even if AV1 Main Profile allows both 8 and 10 bit-depth. Almost all movies and TV shows are delivered to Netflix at 10 or higher bit-depth. Using 10-bit encoding can better preserve the creative intent and reduce the chances of artifacts (e.g., banding),” the company said.
Netflix said it employs “a stream analyzer embedded in our encoding pipeline which ensures that all deployed Netflix AV1 streams are spec-compliant. TVs with an AV1 decoder also need to have decoding capabilities that meet the spec requirement to guarantee smooth playback of AV1 streams.”
To roll out AV1 encoding at Netflix scale the “video encoder searches the parameter space allowed by all encoding tools and finds the one that yields the best result. With a larger encoding tool set than previous codecs, it was no surprise that AV1 encoding takes more CPU hours. At the scale that Netflix operates, it is imperative that we use our computational resources efficiently; maximizing the impact of the CPU usage is a key part of AV1 encoding, as is the case with every other codec format.”
Netflix said that encoding its entire catalog will take time and the catalog rollout strategy will take into account the most popular titles and other factors in prioritizing which shows are encoded in AV1 before others.
To ensure distribution quality, Netflix will also employ new advanced tools to monitor the launch of AV1 streaming, “covering a wide range of metrics from streaming quality of experience (“QoE”) to device performance. These dashboards allow us to monitor and analyze trends over time as members stream AV1. Additionally, the Data Science and Engineering team built a dedicated AV1 alerting system which detects early signs of issues in key metrics and automatically sends alerts to teams for further investigation.”
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By Greg Tarr
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