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M&E Journal: Ultra HD Blu-ray Brings Forth Ultra-Workflow Challenges

M&E Journal: Ultra HD Blu-ray Brings Forth Ultra-Workflow Challenges

Bhanu Srikanth, Giant Interactive

Ultra HD Blu-ray is technically an extension of Blu-ray from a standardization perspective, but it has necessitated extraordinary changes in the post-production workflow in every phase of the production process.

Unlike Blu-ray, the Ultra HD Blu-ray specification supports High Dynamic Range (HDR) color space, which allows a greatly increased contrast between light and dark images on the screen. The result is a much more realistic image. The HDR specification provides for a default 10-bit HDR that supports increased color space (Rec. 2020), with other optional HDR formats available. The specification defines parameters that make up this information, but it doesn’t define a standard format for exchanging this data.

For the enlarged HDR color space to work precisely within the disc mastering workflow, information from mastering such as range of luminance levels used need to be incorporated much earlier in the production process, affecting both video compression and authoring protocols.

Menu design also needed an overhaul to accommodate both the graphics plane’s HD resolution and its visibility against HDR background video. The graphics plane in Ultra HD Blu-ray is not in 4K resolution; it’s still high-definition (1920×1080). Upon playback, menu graphics will be automatically scaled to 4K (3840×2160) by Ultra HD Blu-ray players, compelling designers to conceive and create menus that will not lose integrity with up-scaling.

The design also needs to take into account the perceptibility of the menu against both a High Dynamic Range video, as well as down-converted Standard Dynamic Range (SDR) video when playback doesn’t occur on HDR displays.

Subtitles

This same concern also applies to subtitles. The industry tackled this in a different way, however, since most subtitles have a consistent look and usually employ only one or two colors. To avoid changing the subtitle workflow, tools were developed to enable automatic conversion of the subtitles from SDR to HDR at the authoring stage.

Quality control

Both authoring and quality control (QC) departments also have to reckon with the increased quality checks needed for Ultra HD Blu-ray discs. With previous formats, video QC was predominantly about checking for blocking or artifact issues in compression; now there are the additional concerns of proper color reproduction and brightness levels.

This issue alone is complex and nuanced. Various settings in both the player and television can affect the output differently, which can lead to a disappointing consumer experience. Modern displays in consumer homes fall under one of three categories – SDR/ HD, SDR/4K or HDR/4K displays.

Quality control reviews must check against each of these types of displays. Complicating matters further, the Ultra HD Blu-ray specification allows for authoring to use one or all three optional HDR-to-SDR technologies or even leave the choice to the playback device. To ensure good picture quality across all players, televisions, and various settings, quality control must check all of the different combinations so that the original intention of the content creator is preserved with respect to color, brightness, and conversion.

To accommodate the larger data requirements of 4K video, Ultra HD Blu-ray Disc configurations have also adjusted, supporting larger 100 GB, 66 GB, and 50 GB disc capacities. In production, authors must consider how to optimize each disc layout to maximize player performance. To accommodate a higher bitrate, a special logical layout called “dual zone” can be used.

It places the higher bitrate content on the outer area of the disc, enabling the player to read more bits at a time. Although this feature doesn’t affect the workflow drastically, the option to produce a dual zone disc needs to be considered carefully in the planning stage. Switching to a dual zone configuration at a later stage can have an enormous impact on the timeline. Much of the content will need to be re-encoded, the disc image rebuilt, and all quality checks repeated.

Security

Adding to all these workflow changes is the introduction of AACS 2.0 in the Ultra HD Blu-ray specification, which provides increased protection against unauthorized duplication or transmission. If an Ultra HD Blu-ray title uses the newly enabled, advanced features such as forensic watermark and correction keys, the workflow will undergo further changes as these affect the way the video is encoded and a disc is built and tested in a very fundamental way. Currently several facilities including my company are n testing out these features in order to understand how and where the changes must happen.

Creative now needs to consider designing menus against Standard Dynamic or High Dynamic Range video and must ensure the design stands up to the required scaling. Subtitles need to be adjusted to ensure they are perceptible against HDR video. Mastering metadata needs to be communicated to compression and authoring. Quality control’s scope has increased vastly; content needs to be tested on different types of displays, as well as different player settings in concert with each display.

Format evolutions such as HD to UHD do considerably disturb preexisting processes and workflow, but who is complaining when the result is such a stunning improvement in picture quality and viewer experience?

Certainly not movie lovers everywhere!

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