Preparing for HEVC, 4K Test and Monitoring

Malateshgouda Karegoudar, Tektronix

ALEXANDRIA, VA. Significant change is on the way for the entire broadcast ecosystem. In order to accommodate 4K/UHD transmissions, the way in which video is compressed for transport must improve dramatically. The migration from MPEG-2 and AVC/H.264 to HEVC/H.265 will open up new opportunities, but will also come with risks and potential hidden costs that could neutralize the savings in transmission costs.

For many broadcasters, cable operators and other video service providers, the 4K/UHD transition offers a way to differentiate their offerings from the competitors and generate new revenue streams. However, getting to that point will require a dedicated focus to find the right compression encoding schemes, and potentially significant upgrades to Quality of Service and Quality of Experience monitoring, as well as many other infrastructure improvements.

High Efficiency Video Coding (HEVC or H.265) is designed to deliver the same visual quality as Advanced Video Coding (AVC or H.264), while using about half the bandwidth. It supports all current resolutions including 4K and 8K, and will allow content distributors to deliver HD video to mobile devices over mobile data networks at reduced bandwidth costs, as well as enabling delivery of 4K and beyond video to the home. HEVC addresses essentially all existing applications adopting H.264/AVC, while offering higher video resolution and increased use of parallel processing architectures.

Cutting the cost of transport by squeezing the same data into fewer bits can offer savings, but that doesn't change the fact that 4K streams will raise costs in other areas. For instance, it costs more to ingest, encode, store, protect and transcode more densely compressed HEVC data flows. Although bandwidth is important, it is just a portion of the overall cost of any video workflow.

The big question then is whether making the move to 4K will make sense, not just from a technical perspective, but from a business perspective as well. Some question if 4K will capture the attention of consumers, while the move to HEVC will require that Apple and Android include HEVC support in their devices. Encoders and adaptive bitrate streaming (ABR) software providers, to name a few, need to be onboard as well.

However, there is also a good case to be made for 4K, most notably for its stunning video quality, which always seems to win consumers' hearts and minds. One organization that sees a first-mover opportunity is DirecTV, which became the first multichannel video provider to offer commercial 4K when it launched a new 4K video-on-demand service in December 2014. DirecTV plans to offer more than 30 UHD titles to its 32 million subscribers in the U.S. and Latin America. Netflix is also offering 4K streaming of some programming, notably its House of Cards series.

Other signs around 4K are positive as well. ABI Research, for instance, predicts that five percent of televisions in North American will be 4K capable by 2017. That percentage is expected to double by the end of the following year. The ultimate conclusion is that the industry must begin planning for an HEVC and 4K world.

Tektronix Sentry test system

When considering the move to HEVC and 4K, it's critical to invest in quality monitoring tools. Pretty good 4K misses the point: it's either awesome or not good enough. Consumers who pay a premium for 4K expect a premium product. If a subscriber is paying for 4K and what they receive is the same as HD in the past, there will customer satisfaction issues. As such, the QoE on 4K will be even more critical than it is today.

But the situation isn't as bad as it might seem. Upgrading systems to deliver UHD images can have benefits in other areas. A system that has been upgraded to monitor 4K quality is better equipped to monitor standard-definition and HD streams. Such system-wide improvements are likely to lead to happier subscribers overall, making the investment more easily justified.

GETTING A HANDLE ON HEVC

Video compression standards, such as HEVC, are complex and involve many elements vitally important to the efficiency and interoperability of compressed video in different applications. Therefore, it is critical to use an analyzer that provides verification of the compliance of the stream against the compression standard, detailed analysis and statistics of the video and audio streams, tools for editing and debugging the stream, fidelity comparison against the original uncompressed stream, and the ability to check for any video and audio delay. This allows video designers and engineers to test compliance, interoperability and performance of various compression products.

Efficient encoders are critical for achieving the projected bitrate reductions for HEVC while maintaining quality. When comparing video encoders, it's helpful to have statistics from different encoders for the same quality of video, for instance, to see if each of them is producing a compliant bit-stream or if there are buffer violations while decoding that can affect the decoder, among other factors.

HEVC is a block-based codec, consisting of bigger blocks of coding tree units (analogous to macroblock) that has their size selected by the encoder. The encoder decides to use larger coding units where there is little or no encoding needed (more compression) and picks smaller coding units where more encoding is needed. The size of coding units can vary from 16, 32 or 64 samples, with large size enabling better compression.

A video frame in HEVC consists of many coding tree units, which in turn is built up from coding units. Any coding tree unit or coding units will have different encoding parameters chosen by the encoder. Analysis tools can provide insight to how the encoder is operating.

For example, a CU-size distribution gr

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