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High-quality encoding

Jul 1, 2008 12:00 PM, By Stephane Blondin

Sophisticated solutions preserve the quality of your assets.

Media companies today must work with assets in the file-based domain if they want to take advantage of the latest in IT-based technology. High-quality encoding is one of the key factors in preserving the integrity and value of these assets, which may undergo dozens of encoding processes before they reach the target consumer.

From ingest or encoding in a digital camera during production through to final encoding for broadcast or delivery via VOD, mobile phones, portable media players or Web publishing, numerous processing stages threaten to compromise the quality of the media asset.

If the encoding quality is poor, each encode chips away at the quality of the original material. Downstream versions inherit the flaws of the parent asset, so even small issues upstream can become serious problems downstream. This may result in a financial consequence if the producer or broadcaster feels that quality levels have fallen below an acceptable threshold. Because the value of an asset is tied to its quality, reliable encoding of the best pictures for the target bit rate is critical to any media organization's success.

Formats and workflows

Of the video codecs currently in use, MPEG-2 and DV account for the majority of SD production encoding. HD is a more complicated matter because of its demanding data rate, and different requirements for audio and metadata. While uncompressed HD offers exceptional image quality, the sheer volume of data involved makes it difficult to maintain an efficient workflow in post production.

This problem led to the development of various codecs intended to reduce bandwidth, and therefore storage requirements, while still providing images worthy of being called HD. MPEG-2 (including Sony's XDCAM HD), Panasonic's DVCPRO HD and AVC-Intra, Apple's ProRes 422, VC-3 (including Avid's DNxHD implementation) and JPEG2000 are among the many popular video codecs used for HD work.

Many codecs build on knowledge gained with MPEG-2 development and deal with high-frequency detail, high motion, diagonal detail, gentle gradients and small moving objects in large areas with specific tools to prevent blockiness and other failures that can happen in MPEG-2 systems.

Another downside to working with some newer codecs is that they are considerably more sophisticated than MPEG-2, requiring more hardware and causing software systems to perform more slowly than when working with MPEG-2 content. Furthermore, a lot of interoperability work has gone into MPEG-2 over the past 15 years. Newer solutions may not yet provide as many options or as much interoperability as more mature codecs.

In designing a new facility and choosing a compression format, the content owner or producer must determine the way in which that compression format will be used. A news organization, for example, will often be limited by the capabilities of its newsgathering cameras and the formats supported by its main editing system. As a result, news and sports broadcasters have clear constraints about which format they will choose. More challenging is the design of a production environment, with tape, live feeds and archive material needing to be ingested and converted to the appropriate format.

Each codec has advantages depending on the lifecycle of content within the facility. Is quality for long-term archives most important, or is the goal to get media to air as quickly as possible? Many companies are waiting out the HD compression battle, working with MPEG-2 and using an advanced encoder to transcode into alternative HD formats, as necessary.

If the facility chooses to work with a compression-agnostic wrapper such as MXF, it can more freely build assets and later decide about moving to a newer compression format. Reliance on MXF allows a facility to create transcoded content efficiently and, with the help of metadata, manage media files as simply as a factory manages inventory.

What's more, MXF preserves a history of metadata and media essence, thus providing a future migration path for facilities building a store of MXF masters. As compression formats change, the encoder's MXF support enables the facility to evolve and adapt smoothly to these developments. The Advanced Media Workflow Association is actively working on the use of MXF in automated IT facilities. This work welcomes user input, and companies are encouraged to check the association's Web site (www.amwa.tv) and participate.

The ability to monetize assets through new distribution channels depends on the encoder's ability to support virtually every major format needed for markets as diverse as broadcast, video on demand, portable media players, mobile and the Internet. Encoders that take advantage of a broad spectrum of codecs and use wrappers such as MXF can provide the right content for all these distribution channels while keeping operations relatively simple.

Streamlining workflows

The programming viewers see on TV may have been encoded up to a dozen times on its journey to the home. During production encoding, today's facilities often acquire SD and HD content using digital cameras but frequently end up transcoding to a different format, sometimes unknowingly, as they begin the editorial process. While some facilities edit in the same format used for video capture, more often, the content acquired is converted and transcoded (up-, down- and cross-format converted) to meet the facility's production and editing needs.

Once edited, content may sit in another format on the company's nearline archive, after which it may be encoded again for the broadcast server. Then it's encoded once more when compressed for delivery as part of a cable, satellite or terrestrial broadcast offering. Advanced encoding systems preserve picture quality and simplify the production workflow by providing immediate content access. Figure 1 shows a typical production encoding workflow. Figure 2 illustrates the convenience offered when input, output and conversion work is performed within full automation support. Support for native NLE formats enables fast conversion outside of NLE systems, when required, so that creative staff can get right to work on encoded material.

As content owners and distributors are increasingly called upon to provide premium HD content, advanced encoding takes on a vital role in maintaining the quality of that material. This can be easily understood when realizing that although HD typically offers 6X more pixels than SD, it usually only gets twice the bit rate used today in SD by most people.

A big part of the value proposition for HD rests in its ability to deliver a submersive experience through the quality of picture and sound. So, when addressing HD ingest, the quality of throughput and reliability of ingest are far more critical than in earlier-generation, SD-oriented ingest workflows. While it becomes increasingly difficult to control media as it moves through the marketplace, media companies can use intelligent encoding solutions to make sure that any content they ingest, store, repurpose or distribute meets a high-quality standard.

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