Netflix revealed how the implementation of HDR-VMAF has enabled it to optimise its HDR encodes.
In a blog post, the Netflix technology team said its invention of Dynamically Optimised (DO) encoding has helped the streamer achieve optimised bitrate-quality tradeoffs depending on the complexity of the content.
The company has developed its own HDR variant of VMAF (HDR-VMAF), which it said has enabled it to create HDR streams with DO applied.
Prior to the development, Netflix was using a fixed ladder with predetermined bitrates — regardless of content characteristics — for HDR video streaming, added the post.
The technology team A/B tested HDR-DO encodes in production in Q3-Q4 2021, followed by improving the ladder generation algorithm further in early 2022. They went on to begin backfilling HDR-DO encodes for existing titles from Q2 2022, with the entire HDR catalogue optimised by June of this year.
The blog post adds that HDR-VMAF is designed to be format-agnostic and measures the perceptual quality of HDR video signal regardless of its container format.
“HDR-VMAF focuses on the signal characteristics (as a result of lossy encoding) instead of display characteristics, and thus it does not include display mapping in its pipeline,” added the technology team. “Display mapping is the specific tone mapping applied by the display based on its own characteristics — peak luminance, black level, colour gamut, etc. — and based on content characteristics and/or metadata signaled in the bitstream.”
The move to HDR-VMAF means that Netflix is able to offer its customers 40 per cent fewer rebuffers, lower initial bitrate, and lower internet data usage, especially on mobiles and tablets.
The full blog post is available to read here.
