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04.01.2003
Originally featured on BroadcastEngineering.com
MXF: becoming a standard

From the looks of things, MXF will be one of the subplots of this year’s NAB convention, with numerous manufacturers, including Avid Technology, Panasonic, Pinnacle Systems, SGI, Snell & Wilcox, Sony, Thomson Broadcast & Media Solutions, and others, announcing support in their product lines.



Snell & Wilcox has built MXF capability into their PCI plug-in card range and Ingest station.

The MXF format is built on the existing Advanced Authoring Format (AAF) and uses the same underlying object model that AAF uses to represent time, structural metadata, timecode and any other program descriptor data. While AAF is optimized for the post production industry, where complex projects are interchanged between editing, coloring and CGI stations, MXF is a "flattened" version of AAF, designed to move content between different servers for ingest, playout, rough-cut editing, and into / out of post.

This simplification of AAF was done to allow features such as streaming and partially restore functions, according to Bruce Devlin, a vice president of new technology at Snell & Wilcox. He has written 10 of the 14 signature white papers on MXF and has edited all of the others. “There is a very close association with the AAF, and we have a Zero Divergence Doctrine (ZDD) in place to prevent divergence between the formats creeping in,” he said. “In fact, many of the prominent companies in AAF are also prominent companies in MXF (such as Snell & Wilcox, Sony and Thomson).

MXF is designed for interchange of finished material such as programs, commercials or news stories. Devlin said the required documents are nearing completion as SMPTE standards. These documents--describing D-10 MPEG, D-11 MPEG, DV compression, and simple clips--have passed through the SMPTE balloting process, while work on long GoP (group of pictures) MPEG, VBI transport, editing capabilities, and rich metadata is currently moving forward.

Devlin said that the development of MXF started several years ago, in Europe, with a project called "Generic Format for storage" (G-FORS), that is now completed. It began with an idea that “what if you could create and send a digital file as easily as you can email?” MXF has since evolved to include economical ways of storing files and the reliable interchange of broadcast material as well.

“The [G-FORS] project adopted the MXF format, after about a year of work, after evaluating other formats, and evaluating the effort involved in creating a custom format,” Devlin said. “MXF seemed the best candidate in terms of technical performance and political acceptability.”

There is no license fee for manufacturers using MXF in their products. The many contributors have privately agreed to these terms and the Pro-MPEG Forum is looking at legal ways to formalize the arrangement. “No one to our knowledge has filed any patents directly associated with MXF. There may, however be patents involved in the underlying compression formats, such as MPEG,” Devlin said.

To be compliant with MXF, an application must create a file which is in accordance with the MXF File Format Specification (SMPTE 377M). The use of the format is constrained according to an Operational Pattern (e.g. OP1a is a tape replacement type of constraint and is SMPTE 378M.) The Essence needs to be wrapped correctly, according to the Generic Container specification (SMPTE 379M) and its own mapping document (e.g. Long GOP MPEG is mapped in SMPTE 381M). If the application needs to add Standardized Descriptive Metadata, then the DMS-1 scheme (SMPTE 380M) will be needed.

Going forward, Devlin said that the MXF documents have passed their Technical Approval stage within SMPTE, but still need to go to Trial Publication before they become a ratified standard. There is a small procedural holdup at the moment because some of the numerical values within the standard are defined in the SMPTE dictionary, but have not yet passed technical ballot themselves. Once these procedures have been completed the MXF standard will become fully ratified.

The Pro-MPEG Forum will soon launch an MXF Implementation Group to help manufacturers create MXF applications, devices and to share MXF knowledge.

At the NAB convention in Las Vegas, beginning on April 6, there will be several demonstrations relating to MXF. First, there will be interoperability demonstrations organized by the Pro-MPEG Forum, in room S230 (between the North and South Halls of the LVCC) where companies will demonstrate how they exchange and share MXF content. There will also be a demonstration of live MXF production at booth SL2306 where the European Nuggets project, www.ist-nuggets.tv, will show live transfers of MXF files across a wide area network simulator using IP. The Nuggets project (headed up by Snell & Wilcox and Thomson) will also be presenting a paper in room N109 at 11 AM on the issues involved in the use of live MXF. In addition, the Pro-MPEG Forum will also hold a joint press conference with the AAF association to explain progress in MXF, AAF and their use with other groups such as TV-anytime.

For more information visit www.ist-nuggets.tv and www.snellamerica.com/.

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