Standard being implemented across production chain
The Material eXchange Format (MXF) offers the promise of seamlessly interchanging audio and video material along with associated data and metadata among different manufacturers' equipment. An open standard, the format is available to all, with even free developers' kits available.
MXF provides a wrapper for content, or "essence," in which a description of the essence resides. The MXF file doesn't care what, if any, compression scheme is used on the essence, but it does provide identification of the compression scheme (and many other aspects of the essence) in the form of metadata, allowing a way for that information to be available to applications or equipment.
"MXF tries to solve the file format wrapper problem, to describe how to map a certain essence. It doesn't try to solve the essence conversion," said Tim Claman, Director of Interoperability and Standards, Avid. MXF can be used for file transfers or for streaming across different computer operating systems and networks.
MXF Development ContinuesThe MXF standards fill up more than 700 pages in more than 20 different documents. Devlin said that some developers have interpreted the specs "just a bit differently," and that there has been some ambiguity.
Based on these discoveries, "we are bringing MXF up to date," Devlin said.
In early March, a series of SMPTE standards meetings took place to address outstanding issues. "There was a good bit of progress in SMPTE and we managed to create a new MXF group to look at interoperability," Devlin said.
According to SMPTE, the MXF Working Group will promote interoperability between MXF implementations. It will provide a platform for users and industry to pose questions and requests for guidance and best practices on MXF implementation, analyze ambiguities leading to MXF variations and propose solutions, identify areas where new MXF standards are required, as well as provide adequate SMPTE due process specifications.
In addition, the working group will prepare a test and measurement guideline, provide a liaison with the AAF, respond to ZDD (Zero Divergence Doctrine) issues, and maintain up-to-date MXF status information on the group's Web site ( www.smpte-mxf.org), which is expected to be online in early April.
On the AAF front, Ed McDermid, vice president of business development, North America, Siemens Business Services Media, and director of marketing, AAF Association said that the AAF Association "will deliver the AAF Developers Toolkit Version 1.2 in Open Source, which will include the ability to read and write MXF files. This functionality will be freely licensed to software developers everywhere and available as source code that can be used and modified for developing AAF and MXF applications."
Companies have reported good cooperation among themselves in resolving outstanding issues.
"MXF is the first professional file format that the whole industry can get behind," Kovalick said. "As complex as it is, it is our best choice. The issues of compatibility--they are all solvable.
-- Mary Gruszka
MXF was derived from the Advanced Authoring Format (AAF) data model, and according to the Zero Divergence Doctrine (ZDD), "unless there's a really good reason to make them different, they shall be the same," said Bruce Devlin, vice president, technology for Snell & Wilcox.
Devlin said that MXF stops at cuts-only edits, while AAF is meant for interchangeability throughout the entire post-production process. "By design, we limited what MXF could do."
The implications of MXF implementation to the industry are many.
"It's not just going to HD that's the end game. It's the move to a more IT-centric environment, with the ability to pass metadata around," said Joe Zaller, vice president of strategic marketing and product management for Snell & Wilcox. "With MXF, we are moving away from proprietary systems. If people are locked into proprietary systems, it's very expensive and you need highly specific equipment to interface with. MXF provides the ability to integrate into an IT system."
Over the past year, there has been remarkable progress in implementing MXF in products designed for the whole workflow spectrum--from acquisition to editing, to server storage and distribution, and for archiving.
"What we are seeing is MXF is being adopted very quickly and broadcasters are demanding it," Zaller said. "It will be interesting to see who is not making MXF products."
ACQUISITION & EDITING
Both the Sony XDCAM and Panasonic P2 camera acquisition formats provide MXF files; but there are differences. The obvious one is the encoding of the essence within the MXF wrapper--Sony XDCAM uses IMX encoding, and P2 uses DVCPRO. But there is another difference as well--the MXF operating pattern each company chose to use for its format.
Operational patterns (OP) allow for the huge flexibility of MXF, representing different package and item complexities, for example, a single source clip or multiple source clips for alternate versions of the same program. Item complexity can be designated as single item (1), playlist items (2) or edit items (3); package complexity can be called single (a), ganged (b) or alternate (c). OP designations range from 1a to 3c, plus OP Atom.
Operating pattern Atom separates the video and audio essences into multiple files but with a common clip metadata for all the files. OP1a interleaves audio and video tracks into a single file.
How these two variations affect interoperability with nonlinear edit (NLE) systems depends on who you talk to.
"There are no issues with nonlinear editing," said Hugo Gaggioni, chief technology officer, Sony Broadcast. "We use OP Atom inside XDCAM, but when we play out content, we format it to put it in interlace to be viewable by humans."
Gaggioni said that XDCAM is compatible with Avid, Grass Valley, EVS, Quantel, Pinnacle, Leitch, Omneon and SGI.
In general, makers of NLEs currently support or will support both P2 and XDCAM formats.
Pinnacle Liquid, for example, uses an import function to bring in XDCAM or P2 files to the NLE and separate the audio and video tracks, according to Al Kovalick, strategist and Pinnacle Fellow, Pinnacle Systems. Editors scan and browse which files they want to import. "We don't use the Sony thumbnails," Kovalick said, referring to the thumbnails that the XDCAM format provides. "Liquid outputs [an MXF file in] OP1a."
Avid uses OP Atom as the native MXF format for its edit products. "For complex edits, video and audio need to be separate files," said Claman.
"You can plug a P2 card into an Avid NewsCutter and immediately edit," said Phil Livingston, vice president, technical liaison for Panasonic Broadcast. "The power [of OP Atom] is that it can be edited instantly, which is not true for MXF operating pattern formations that need to be parsed."
There is no actual ingest per se, Claman said. "You don't need to import or convert to look at the file."
For Avid to be compatible with XDCAM, "we had to do some work to read Sony's files. It didn't just magically happen," Claman said. "We can't directly edit the XDCAM disk, but we're able to very easily integrate with XDCAM. We convert [the files] to another operational pattern as an import step. We also had to make an MPEG codec to read the [XDCAM MPEG-4] proxy files."
Avid now provides a transfer agent to output the finished program as an OP1a MXF file, Claman said.
Gaggioni said that it's a fairly trivial issue to convert XDCAM to Avid. "It's done on the fly," he said. "You have to unwrap the material and get the essence out. It's a nonissue at this point."
Other gear used in the editing environment, like character generators, are also going MXF. Pinnacle, for example, provides MXF support for DV25 and MPEG up to 50 Mbps, all in SD for Deko graphics CG and Thunder live production server, Kovalick said. "HD versions will be shown at NAB2005 with support for MXF for MPEG only. In Liquid we support MXF for MPEG and DV."
Next in the workflow chain are the servers for storage, distribution and playout. Most servers today support OP1a, with some companies developing additional support for other operational patterns. "For a playout server you want one file for the finished story where the audio and video are interleaved," Claman said.
Some servers store files as MXF native; others wrap other file formats inside an MXF wrapper.
Thomson Grass Valley provides the UIM, Universal Interface Module, to support MXF for older servers. "The interface package makes our older servers talk over Ethernet and talk over MXF," said Ray Baldock, chief technology officer, Thomson Broadcast & Media Solutions. "This has been popular with our existing customers to get them into MXF without replacing their servers," he said. Thomson Grass Valley also supports its GFX file format.
Avid is "using MXF as a native file format and also for exchanging files with other vendors," Claman said. "It gives us a new native file format internally at Avid and media files that are open to anyone to look at them."
Historically Avid stored its files as OMF, but not all Avid products, notably Pro Tools, could create them (although they could read them). Avid will continue to support OMF for compatibility with legacy products.
At NAB2005 Sony will introduce a new server with new architecture that will be purely native MXF, Gaggioni said.
For the Omneon Spectrum server, "the code for full MXF support of OP1a was released about a year ago," said Adolfo Rodriguez, director of product marketing, Omneon Video Networks. "We will be improving on that in the next few releases with the addition of more operational pattern support."
According to Rodriguez, the initial "container package" for the Spectrum server is MPEG-2, specifically IMX. "This was driven by the [Sony] e-VTR, the 1/2-inch tape machine that could record natively I-frame only MPEG-2 IMX, 30, 40, or 50 Mbps," he said. This format is also compatible with XDCAM.
Pinnacle put its first MXF MediaStream server on the air 15 months ago at French broadcaster Canal Plus, Kovalick said. "Since two years ago, we decided within the company that every product built is to be MXF-compliant," he said. "If we can build a product that is MXF-compliant and compatible, we can build more interesting solutions."
Leitch servers now support MXF, according to Todd Roth, vice president, technology, Leitch Video Servers. "Overall MXF is in a "beta-test" stage," he said. The Leitch Nexio server processes MXF files while storing the media natively as non-MXF.
"This more complex approach requires complete parsing of files on input, and generation of MXF containers, headers and metadata keys on output," Roth said. "The advantage of this approach is that different processing techniques can be used, depending on file source or destination. There are too many variables within the MXF file to assume that a single, unchanged file will work in all situations and source/destination combinations. In reality, this additional configurability and complexity is required to make the different MXF implementations work."
Roth said that this approach also takes into consideration metadata workflow. "Metadata needs to change [along with essence] at each process within a given workflow," he said. "Not only do these changes need to encompass what is done at each particular stage, but the requirements of the next (previous) device in the chain."
One implication for MXF deployment is that it may help do away with the ingest server altogether, according to Zaller. An example is the Snell & Wilcox Comet turnkey ingest solution that Zaller said is based on open standard ingest tools and low-cost storage. "This is an example of a product that is IT aware," he said.
Transformed by MXF, archive systems will become simpler, nonproprietary, more flexible and less expensive. That prediction was made by Phil Ritti, vice president, and general manager, Quantum Media Division.
At NAB2005 Quantum will introduce an MXF tape drive, the SDLTv. "The new drive will be like a data NAS," Ritti said. "You can see files as soon as you put the tape in, and drag and drop files. And you don't lose metadata. It's very straightforward to integrate on a network. You don't need all the extra software to get there. Now you have media that you can take anywhere."
Contrast this with the way archives are currently built, with layers of software, an archive manager and SCSI drives. "If one piece goes away, you can't get at your media," Ritti said.
The Quantum SDLTv is enhanced to work with MXF files. "You can store any kind of file with this device," Ritti said. "It pulls key metadata out of the MXF header and stores that in a directory, which you can then look at. The most powerful thing it does is when given a starting and ending timecode, it will create a new MXF file with just that piece of essence in it and hand it back to you."
Companies developing MXF products reported using a variety of tools, from home-grown to those from outside providers.
At NAB2004, Snell & Wilcox made headlines with its free distribution of the MXF Express developer's toolkit and MXF Desktop, which allows users to play back and examine MXF files.
"We're excited about the response to MXF Express," Devlin said. "There are over 1,200 users registered, and there's not one typical user. We have also created the most active MXF discussion site, our forum on our Web site [ www.snellwilcox.com/mxf/]."
For NAB2005, Snell & Wilcox will update both of these packages, Devlin said. MXF Desktop will add visualization tools so users can see how the file was put together. These same tools will be added to MXF Express, along with updates for interoperability with different vendors' products.
Customer expectations for MXF have been high, Claman said. "Users expected to pick up files and move them, but that's not always the case. MXF is a relatively broad standard; there can be different types of legal MXF files, and it's relatively early in the maturation process. Over time the divergence will subside some. But it won't happen overnight."
Although there are still some interoperability issues to be hammered out for the MXF standard itself--metadata, vertical blanking interval, to name two--"customers may have been expecting codec compatibility as well and assumed a library of codecs tied to MXF," Claman said. An MPEG encoder isn't going to read a DV file, no matter how compatible the MXF wrappers are.
"MXF doesn't make a product do more than is capable," said Bob Edge, Chief Applications Engineer, Thomson Broadcast and Media Solutions. The essence has to be compatible as well. "But at least you can see what the format is before transfer."
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