As consumer HDR displays have differing peak luminance and contrast capabilities that are not infrequently less than the mastering display, it’s necessary to map PQ content to match the capabilities of the target consumer display device. This scaling or mapping is controlled and managed by metadata. According to YouTube’s help page,
“HDR videos must have HDR metadata in the codec or container to be played back properly on YouTube. Once a video has been properly marked as HDR, uploading it follows the usual process of uploading a video. YouTube will detect the HDR metadata and process it, producing HDR transcodes for HDR devices and an SDR downconversion for other devices.
To be processed, HDR videos must be tagged with the correct:
- Transfer function (PQ or HLG)
- Color primaries (Rec. 2020)
- Matrix (Rec. 2020 non-constant luminance)
HDR videos using PQ signaling should also contain information about the display it was mastered on (SMPTE ST 2086 mastering metadata). It should also have details about the brightness (CEA 861-3 MaxFALL and MaxCLL). If it’s missing, we use the values for the Sony BVM-X300 mastering display. Optionally, HDR videos may contain dynamic (HDR10+) metadata as ITU-T T.35 terminal codes or as SEI headers”.
DaVinci Resolve is able to generate this metadata for us. After you’ve finished grading your video, you can go ahead and add MaxCLL (Maximum Content Light Level) and MaxFALL (Maximum Frame Average Light Level) HDR10 metadata. MaxFALL expresses the value in nits for the frame in your project with the highest average brightness level, while MaxCLL is the value, expressed in nits, of the brightest pixel component in the project. In Project Settings on the Color Management page, check Enable HDR10+.
When the viewing aspect ratio and the image aspect ratio are different, blanking is required to set the image area for HDR10+ analysis. Go to Timeline – Output Blanking and select the correct aspect ratio.
Next, on the color page, select the Color tab > HDR10+ > Analyze All Shots.
Be sure to deselect Tone Mapping Preview in the HDR10+ pane at the bottom left of the color page.
On the Deliver page, check Embed HDR10 Metadata.
If you check Export HDR10 Metadata, a document will appear alongside the video file. In order to open it, change the suffix to mov.txt. The document will look something like so:
The metadata includes information about chroma subsampling and bit depth (4:2:2 10-bit), color primaries (BT.2020), transfer matrix (PQ), matrix coefficient (BT.2020 non-constant), mastering display color primaries (P3), mastering display luminance (min: 0.0001 cd/m2, max: 1,000 cd/m2), MaxCLL and MaxFALL.
Skeptical that MaxFALL measured only 22 cd/m2, we analyzed the clip using the display qualifier focus setting in the video scope option menu of Resolve. As the eyedropper tool is moved around the image, a circle appears in the waveform monitor revealing the sampled pixels, confirming that much of the picture does indeed fall well below 22 cd/m2.
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