Part 3: Live and VOD-to-Live HDR workflows on AWS

Part 1: Expanding the color gamut with HDR and AWS Elemental
Part 2: HDR VOD workflows using AWS Elemental Server and AWS Elemental MediaConvert
Part 3: Live and VOD-to-Live HDR workflows on AWS (this post)

Introduction

In this post, we focus on live content generated in real time, as well as file playout or VOD-to-live workflows where the assets are prepared ahead of time. AWS Elemental Live (on-premises) and AWS Elemental MediaLive (cloud) both support live HDR workflows up to UHD, as well as the ability to down-convert HDR to SDR. These platforms also allow forcing a mix of HDR formats in the input side to a single output type, which can be beneficial downstream.

Workflows

For HDR cloud-based workflows, AWS Elemental MediaLive can receive live sources via HLS, AWS Elemental MediaConnect flows, uncompressed AWS Cloud Digital Interface (AWS CDI) sources, or inputs from AWS Elemental Link, which supports 10-bit video. MP4 assets that live in Amazon Simple Storage Service (Amazon S3) can loop or play out as part of a VOD-to-live workflow.

For HDR on-premises workflows, AWS Elemental Live can receive content via unicast, multicast, SDI, SMPTE ST 2110, SMPTE 2022-6, HLS, SRT, or directly from MediaConnect. Media files upload directly to AWS Elemental Live and play out as inputs for your live event. Optionally, external devices such as an AJA Ki Pro Ultra can handle file playout and feed an AWS Elemental Live appliance via 3G SDI or quad-SDI for UHD sources.

Depending on the scale of your production, live streaming in HDR can present obstacles to overcome in order to keep your color choices accurate. Some cameras, such as many made by Blackmagic Designs, allow you to shoot in logarithmic format and apply a look up table (LUT) in the camera directly, so the output is already PQ or HLG. In some cases, where loading a LUT into the camera is not possible, customers can handle the log to PQ/HLG/SDR conversion using something like an AJA FS-HDR, which is also a great resource to feed your on-set monitors and ensure the look is exactly how the producers envisioned it.

Dolby Vision – workflow

Metadata

If your outputs are HDR10 or Dolby Vision compliant, some analysis is required to extract the MaxCLL and MaxFALL values needed. If you play out a file as your source, you can use a tool like DaVinci Resolve to export the HDR10 metadata when it completes an HDR10+ inspection of each frame. You can review the text file to find the needed values.

If you’re in a live streaming scenario, this becomes more of a best effort. Depending on your event, you can record the rehearsal, or record the sport field before the event begins and run through the same metadata extraction process.

When targeting a Dolby Vision output, AWS Elemental Live is required for the workflow. Since AWS Elemental Live has integrated the Dolby Vision SDK, the software adds the necessary metadata in the outputs where Dolby Vision Profile 5 or 8.1 is selected in the Preprocessors >> Color Corrector >> Color Space Conversion section of the output. Read this deep dive on Dolby Vision for more information.

HEVC & AVC

When dealing with ABR protocols like HLS or DASH, expecting the client player to switch between codecs is not recommended. Many players, such as smart televisions or older USB stick devices, don’t have the CPU necessary to switch between codecs and will buffer or stall completely. Players also shouldn’t switch between HDR and SDR. This can cause a wrinkle when dealing with HDR, as it means you likely need a full HDR ABR ladder, a full SDR ABR ladder, and if you want to support both HEVC and AVC, you likely need a third ladder. This may require using multiple AWS Elemental Lives for the same stack, which requires the Output Locking feature to synchronize outputs at the frame level. Read this walkthrough of Output Locking for more information. Additionally, the mix of HDR and SDR can cause challenges when dealing with SSAI, where the ads may be in SDR, but the program is in HDR. It’s critical to test your players with all the expected variations to ensure smooth playback for your users. Many TVs will allow USB sticks to play back video content, making it an easy way to double check your HDR settings on a TV.

HDR product support reference

AWS Elemental Live:
Inputs: HLG, HDR10(PQ)
Outputs: HLG, HDR10(PQ) and Dolby Vision

AWS Elemental MediaLive
Inputs: HLG and HDR10(PQ)
Outputs: HLG(Passthrough), HDR10(PQ)
The simulated difference between HDR and SDR

Conclusion

In this three part series, we walked through the AWS appliances and services used to add HDR support to your OTT video workflows. Adding HDR can make a major impact to your viewers and elevate your content, but it does require some upfront planning to ensure the color makes it to the screen exactly as it was intended. 10-bit video is key and having both an HDR and SDR monitor helps guarantee an excellent end result.