The Future of Edit Data Exchange
Open Media Framework (OMF) and Edit Decision Lists (EDL)
Brooks Harris - March 1997
As the production industry moves toward non-linear online, digital compositing, and electronic film production the need for sophisticated edit data transfer becomes increasingly important.
Edit data is information concerning source identification (reel names, timecodes, digital media file references) and instructions on combining this source material into a completed production. This information must be organized in the form of a standard exchange protocol so each system can use it effectively.
Each editing environment has its own particular architecture and hence its own particular needs with regard to edit data. For instance, non-linear offline creates effects in its digital architecture in a very different way than the conventional online system will recreate those effects on tape. This requires some method of converting the digitally produced effects information to a usable form for online.Another example is electronic film production, which often includes 30 FPS video production stages before it is ultimately recreated in 24 FPS film. Here, frame-rate conversion becomes critical. Some systems are resolution independent, imposing the further requirement that resolution, image compression and processing information also be communicated amongst systems.
To effectively move data between these editing environments requires a comprehensive data exchange protocol that goes beyond the conventional EDL (Edit Decision List). The advent of Open Media Framework introduces the post production industry to a new era of edit-data processing. This evolving edit data format promises to address these issues.
OMF (Open Media Framework)
OMF is an industry standard for edit data exchange being promoted by, and under development at, Avid Technologies.OMF is an outgrowth of the experience derived from the development of the Avid editing products.
OMF is based on "Bento", an object-oriented "container" database system standard developed by Apple. The beauty of Bento is its extensibility. By defining Bento "objects" almost any kind of data can be handled effectively. OMF, then, is a specification for the use of Bento to describe production and post-production information. It includes specification of object types describing editing data and how to use them.
An OMF file is binary and can be created or read only by applications designed specifically to do so.OMF specifies objects describing such elements as tape sources, edited compositions, effects, and frame rates. It also includes specification on how to reference digital media files for playback, as well as logging and library information. All these elements are linked to one another to describe the entire project.
As a matter of practicality, OMFs created by the Avid Media Composer define the de facto OMF "standard". This is due to the prodigious number of Media Composers now in use. OMF was developed earlier and greatly benefits from the lessons learned at Avid. Consequently, most development of OMF applications have followed the Media Composer example (and, lets face it, its not a bad example to follow).
The current versions of OMF (1.x). work well within their intended working environments but there remain some incompatibility issues between editing systems. The 2.0 specification is significantly improved. Some ambiguities in the original specs have been resolved and new capabilities have been added. 2.0 OMFs will "hit the street" sometime this year and promise to increase compatibilities amongst applications.
At the same time, the development of the OMF Toolkit marches on. Avid provides a programmer's toolkit to the industry designed to make writing OMF programs easier. The latest Toolkit provides a robust, cross-platform, development tool set. Used appropriately, the Toolkit will help enforce OMF compatibilities.OMF is now being accepted. The effective exchange of data between systems in the Avid product line demonstrates OMFs strengths. In view of this, other manufacturers are getting on the bandwagon.
Edit Decision Lists (EDL)
The EDL standard for transferring edit data was originally designed in the early '70s for conventional tape editing, long before anyone had digital media or complex image processing to deal with. But EDLs are ingenious, really. They are simple, small files, yet they embody much of the basic information required to assemble a production . Conventional EDLs remain limited in some important respects. They have no provision for digital media file referencing. They cannot handle more than one layer of effects at a time (dissolves, wipes, keys). Image processing exists only in proprietary implementations of switcher control. They have only four channels of audio. They cannot deal with special frame rates, especially film.
But even with these handicaps, EDLs are very useful. They can hold the basic information about how to build a video program - source scenes and their positions in the show. They describe dissolves, wipes and keys - the vast majority of effects. And they are small and fast. There is a huge installed base of production and editing equipment which use EDLs. Although the attention is recently focused on non-linear editing, the fact is that conventional tape will continue to play a large role in the industry for years to come - it has no storage limitations and it has real-time effects capability. These factors continue to outweigh the advantages of non-linear online in many instances and EDLs work reasonably well in these environments.
The recently completed EDL format, SMPTE Standard 258M, may breath new life into EDLs if edit manufacturers fall in to support the standard. The SMPTE EDL is strictly defined and is able to handle some image compositing with the addition of the "virtual" event concept. This idea goes a long way toward extending EDL's effects capabilities into the modern era. It also extends EDL audio channel capacity to 99 channels. Don't count EDLs out yet.
OMF and EDL
EDLs are simple, fast, and effective. This may be viewed as superior to OMF in so far as their information covers the environment's requirements. OMF can and will be applied to systems currently using EDLs but it will be some time before OMF (or any other "super EDL" format) replaces EDLs completely. They are everywhere, and they are useful. EDLs will remain an important and viable edit data exchange format.But OMF is gaining momentum. It promises major advances especially in dealing with digital media. Major manufacturers are lining up behind it because -
A) The industry dearly needs a format with its capabilities
This means EDLs and OMFs will coexist. Projects will likely use both OMFs and EDLs somewhere in their edit data management path. Many possible needs exist - offlining in non-linear, conforming in online, for example, or integrating graphics into an online.
This gives rise to the need to move edit data between EDLs and OMFs- to extract EDLs from OMFs and create OMFs from EDL s. Avid's use of MCXEDL* in the MCXpress for Windows NTÔ product is an example of this process - the MCXpress records an OMF and MCXEDL extracts the appropriate edit data from the OMF to create an EDL.
The EDL may someday be eclipsed by newer technology but will continue to coexist with OMFs for a long time to come. Say "Good Morning" to the OMF Emperor, but don't forget your poor EDL cousin.
*MCXEDL was written for Avid by Brooks Harris Film & Tape, Inc. using the EDLMAX EDL engine.
Avid, OMF, Open Media Framework and Media Composer are registered trademarks and MCXpress and MCXEDL are trademarks of Avid Technology, Inc. All other trademarks contained herein are the property of their respective owners.