Content preparation for adaptive-bit-rate video

Choosing packaging and profiles

Packaging choice is generally driven by what devices must be supported. Not every device supports players for every type of ABR streaming technology. As a result, one should catalogue both the devices and the players that will be supported. The necessary packaging will naturally become apparent as a result.

The selection of optimal bit rates, frame sizes and frame resolutions will vary depending upon device types, connection types and encoding technology. Apple and Adobe provide excellent starting points with suggested profiles suitable for their ecosystems. However, practically speaking, the entire catalogue of devices, expected network connections and network costs must be considered when designing layers.

With these considerations, layer design is a balancing act between frame size, bit rate and quality. However, the actual encoding technology used may have the biggest effect upon quality. For example, one study performed by the MSU Graphics & Media Lab showed that the use of x264 encoding technology saved necessary bit rates by as much as 50 percent compared to other H.264 encoding technologies at the same quality level. As a result, it is recommended that layers be designed while performing actual encoding tests with the final encoding technology.

Most packages, however, generally contain between 16 and 24 layers. Part of layer design will require a reduction in the number of layers. It is best to select a few common native display frame sizes (such as 1080p) and then encode multiple bit rates to those frame sizes. Doing so will avoid unnecessary performance degradation on players that use software scaling (particularly important for Adobe HDS).

Encoding, packaging, delivery and DRM

Each layer will require that a complete H.264 stream be encoded. With 16 to 24 layers, encoding an ABR package can easily require 20 times the processing power needed for a single H.264 stream. Fortunately, highly parallelized multirate H.264 encoding technology exists that re-uses information across the different streams. When combined with GPU acceleration, today’s encoding systems can offer 10 or 20 times the speed of CPU-based systems.

When preparing for multiple devices, an important aspect of encoding is transmuxing, the ability to re-use encoded H.264 streams across multiple package types. This prevents having to re-encode the same bit rates simply to package the video differently.

With on-demand content, it is important to perform QC checks on the different video streams. QC may be performed visually or by using automated tools that measure quality across all of the streams.

On-demand content often requires user authentication and protection prior to playback, which requires digital rights management (DRM). When using DRM, the video must be encrypted during packaging, typically using AES 128-bit encryption. DRM systems typically have subtle requirements for how the encryption is performed by the encoder or packager, and it is important to validate that the two are compatible.

Finally, content delivery will be performed, either as a compressed TAR file or in the native package form. Where possible, it is recommended that the entire production process (ingest, encoding, transmuxing, packaging, quality control, encryption and delivery) be combined into a single automated workflow. Manual steps will significantly slow production time and may result in errors. It is also recommended that the ABR production process be combined with non-ABR production into a single automated system. This reduces system maintenance costs, offers a single view into the overall content production for all distribution channels and allows workflow efficiencies such as unified metadata preparation and content preprocessing.

Conclusion

Preparing video for ABR streaming generally requires research up front to choose technologies and encoding profiles, and a well-integrated, accelerated encoding approach to ensure workflow efficiency. With today’s tools, it is possible to fully automate the ABR content production workflow with full integration into existing content preparation and delivery workflows.

---

—John Pallett is director of product marketing, Telestream.