Netflix Talks Dolby Vision and HDR10
For our article "Blackest Blacks: Ten Things to Know About Producing HDR," Netflix was kind enough to answer our HDR-related questions in writing, and provided lots of into that didn't make it into the article. These answers were compiled by three different departments at Netflix, hence no individual attribution.
Streaming Media: When you say your HDR sources are Dolby Vision (DoVi), what does that mean? Is that a container format? Codec? Both with metadata?
We ingest Dolby Vision IMF masters. They are IMF with J2K video and Dolby Vision metadata.
Are you using a separate encoder, or did you build HDR into your cloud encoder?
We partnered with Beamr (formerly Vanguard Video) and Dolby to add Dolby Vision support into V265, the HEVC encoder that we use in our UHD encoding workflow (4K Rec. 709, DoVi, and HDR10).
Are you preparing separate encodes for DoVi, HDR10 and Rec709 or can you create a single output that includes two or more?
Dolby tools natively enable deriving Rec. 709 and HDR-10 from the DoVi source. This allows us to produce all of our encodes from the Dolby Vision source. These profiles include the Rec. 709 profiles: CE1 & CE2 (legacy VC1), CE3 (H264), CE4 (10-bit HEVC, and VP9), and our mobile profiles AVC-HiProfile and VP9-M (8-bit), in addition to the CE4 HDR profiles: Dolby Vision and HDR10 (HEVC), and VP9.
Are you doing anything differently for preview/QC of HDR content?
We analyze the HDR alongside the SDR derivative to ensure consistency and that no material differences are present beyond the inherent luminance discrepancies.
Are there any unique controls for DoVi or HDR10 that you have to adjust to produce optimal output? Or is it simply a yes/no switch or something similar?
Many Dolby Vision masters are in P3 colorspace. For HDR10, we have to convert to rec.2020 color space with some processing and a color adjustment. If you are interested in more details, we published this paper that loosely describes how we optimize the quality of the HDR10 encodes derived from the DoVi masters.
Has it been your observation that DoVI/HDR10 support is fairly uniform among all STBs/SmartTVs that support it? If the video looks good on one, does it look good on all?
Are you having to work with camera LUTs or is that all handled before you get the files and normalized somehow in the DoVi source?
Cameras on our productions record in RAW or Logarithmic formats which preserve the full dynamic range of their sensors. The bottleneck has traditionally been SDR displays, which require squeezing and compressing this dynamic range into a much smaller range than was captured. With HDR displays, the scene's dynamic range can be rendered more faithfully, at which point the DP and colorist can explore different creative directions and utilize more (or less) of the display's higher dynamic range. When delivered, the images are 'normalized' in the sense that they are encoded in the mastering display's color space.
Do you have any requirements for how videos are shot and edited for Netflix titles?
We have technical requirements that include a list of approved cameras, recording formats, and best-practices for color pipeline and post-production workflows that are in place to preserve the highest quality from camera to delivery. With regards to shooting, editing, and color grading, we give filmmakers the freedom to get whatever look and feel they envision, so their choices vary on camera, format, and systems, depending on the creative direction they wish to take.
HDR is 10-bit. Does this mean to get the equivalent quality of 4K@16Mbps in 8-bit, you need to encode to 20Mbps?
Our CE4 profiles are all 10-bit whether Rec. 709 or HDR, and our 4K bitrate maxes at 16Mbps. Moving from 8-bit to 10-bit does not significantly impact bitrate. FYI, Dolby Vision is natively 12-bit in the ITP color space. At encode, there is preprocessing and shaping into 10-bit for distribution and then it is mapped back to 12-bit on a Dolby Vision-enabled TV.
What's the bandwidth of the HDR10/DoVi metadata? Is that streamed along with the video?
Both Dolby Vision and HDR10 have static metadata repeated at regular intervals. Dolby Vision also has dynamic metadata. The metadata is typically a very small part of the encoded bitstream such that it is not a factor.
Is HDR production all HEVC at this point? Doing any in H264 or VP9?
As mentioned above, we produce PQ HDR for VP9. Nothing for H264.
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