If you are new to the world of video and largely work inside of a closed environment – such as starting and finishing your DV project all inside Final Cut Pro – then, you have yet to wrestle with the details of exchanging your project information with another piece of software or computer editing system. Before nonlinear editing, video post-production was divided between offline and online editing. This paradigm was borrowed from the film world: editing workprint and lab finishing. The first part was the “messy” creative, decision-making side of editing; the latter was the “manufacturing” of a high-quality product. Meticulous handwritten record-keeping permitted decisions made in the first phase to be used as the basis for the second.
This film workflow was adopted by videotape editors at about the same time that SMPTE timecode was standardized. Timecode permitted a method of electronically tracking edits and moving offline editing data into the online (or finishing) stage of the process. Edit Decision Lists (EDL) have been with us since the 1970’s. They are largely unchanged, yet are still the most frequently used “lowest common denominator” when moving information between various edit systems and software applications. EDLs are simply text documents showing a series of columns, displaying edit event, source reel numbers, type of edit (audio or video), transition type (cut, wipe, key or dissolve), transition duration and the ingoing and outgoing edit points – in timecode – of the source and master tape(s). This type of information is commonly referred to as “metadata”.
Each edit event line is read horizontally and represents a change made to the master tape or sequence at that location on the master. Other information may also be displayed, like slow-motion speeds and editor’s comments. The source reel identification can be up to eight alphanumeric characters, depending on the EDL format (CMX, Sony, Grass Valley). Finally, drop-frame and non-drop-frame timecode can be mixed. Since EDLs can only accurately interpret one track of video and four tracks of audio, they are extremely limited in carrying the information generated by most modern nonlinear edit systems, like Avid or Final Cut Pro. In addition, almost none of the visual effects or audio mixing and panning data can be included within the EDL format.
We have temporarily hit a point in time where the offline/online editing strategy isn’t always needed, so you might ask, “What’s the big deal?” This is only for the short term. For instance, as the industry moves towards greater use of HD, it is once again impractical to start and finish your editing in the same quality and resolution as the final master. A far more cost-effective solution might be to do your creative editing with DV copies of your HD tapes and then go to an HD facility to faithfully recreate that edit in HD. It would be nice to have as much of your audio, effects and color-correction data translate from one system to the other. Since EDLs are very limiting, what are the other choices?
A few years into the development of its product line, Avid Technology tried to get another manufacturers to jump on the bandwagon and participate in the development of Open Media Framework Interchange (OMFI or OMF). OMF files were designed to be able to carry forward more of the information from the edited sequence than EDLs had been able to do. This meant that the vertical track hierarchy of NLEs could be preserved, as well as more of the effects metadata. In addition to just information, an OMF file could also contain embedded audio and/or video media files, permitting an entire edited sequence to be moved in a single archive file.
As promising as this sounds, it proved less effective than hoped for. First of all, the information about how an NLE program applies a specific effect, like a DVE move, tends to be proprietary metadata specific to that maker; therefore, effects information included in an OMF file is largely generic and still has to be recreated on the second system. For instance, the offline editor might have applied a certain DVE move on a clip on track two. The OMF file received by the online editor shows a DVE effect with a default value, but not those originally created. Certain effects, like a “film-style” dissolve might not come across at all. For all of their promise, OMF files have really turned into glorified “super-EDLs”.
There are a few areas where OMF files have proved a great workflow enhancement. Wes Plate – a veteran Avid and After Effects user – founded Automatic Duck with his programmer father. Together they have developed a number of interchange utilities to move files between various NLEs and After Effects. The most notable of these is Automatic Composition Import, which is designed to move layered sequences from Avid or Final Cut Pro into After Effects, while still maintaining the layer hierarchy. Effects have to be recreated in After Effects, but it’s a great starting point. Furthermore, if the NLE and After Effects reside on the same computer or even the same network, no media actually has to be moved. OMF and ACI permit an OMF file to be exported with media linked rather than embedded. This means that After Effects will simply find the location of the Avid or Final Cut Pro media files on the drives without any duplication of media. There is a lot of interest in moving sequence and layer information from an NLE into After Effects, so other manufacturers, like Sony, Media 100 and Pinnacle, each have their own routines for sending clips from their timelines straight into an After Effects project.
OMF has also become the de facto interchange format in the audio world. It is easier to send OMF audio data between competing systems, while retaining information about track patching, mix levels and panning, since audio mixing tends to be a bit less proprietary among manufacturers. The idea is to get the basics across, since the final mix inside the digital audio workstation will most likely use a number of customized, effect-filter plug-ins that weren’t available to the offline editor anyway.
A good offline editor can do a lot to build and clean up audio before sending it to the mixer, which ultimately saves everyone time. Since audio file sizes are fairly small, the embedded multi-track audio for the timeline of a one-hour TV show can fit on a single CD-ROM. It is important to understand that simply creating an OMF for audio isn’t the only step. DAWs like Pro Tools don’t inherently read OMF files, but rely instead on a utility called DigiTranslator (often an extra cost option) to turn OMF files into Pro Tools session files. You also have to be aware of the native audio file format used by your NLE. This varies with PCs (which normally use WAV audio files) and Macs (which tend to use AIFF). Older Macs also used SDII (Sound Designer II) as an audio file format. Most modern PC and Mac DAWs can work with either AIFF or WAV files, but generally PCs can’t deal with the older SDII files.
Since neither EDLs nor OMFs have provided the magic solution, the industry has moved on to the Advanced Authoring Format (AAF). The AAF is intended to provide a far greater ability to share effects parameters and other metadata among different products. AAF’s supporting organization has a larger number of companies who back this standard, than did OMF. In order to get everyone to sign on, the specifications were designed to permit a portion of the code to stay proprietary for each company, if they so choose, so AAF still won’t be totally universal. This means that Avid or Quantel or someone else might still have certain effects that can only be read perfectly by their own systems. For instance, one company’s AAF file might be 90% open and 10% proprietary – another’s might be totally open. It all depends on what they feel will further their position in the marketplace.
Like OMF, AAF has the ability to embed audio and video media as well as metadata into the file. The media subset of AAF is called Media eXchange Format (MXF), which is essentially the file format used by Sony in its MPEG-IMX products. The promise is that in the near future you might be able to shoot with your Sony camcorder and upload that video as a data file into a Sony (or other) server. You then might edit the news story using an Avid Newscutter that could read the MXF file straight from the server without any need to digitize or convert files. In the coming year, Avid products are supposed to be able to deal with both OMF and MXF media files, once the MXF specs are fully standardized. It is important to remember that both MXF and OMF media formats aren’t compression schemes, but rather “wrapper” information that tells an editing system, server, VTR, etc. what type of a file it is, what properties it has and what to do with it.
It isn’t specifically the same type of interchange format as OMF or AAF, yet Apple’s QuickTime has proven to be one of the better methods for moving files between various applications and platforms. QuickTime can support various frame sizes, frame rates and compression schemes, up to and beyond uncompressed HD. Even if a computer can’t fluidly play a high data rate QuickTime movie, it can still pass it along. QuickTime, like the other media formats, is a media “wrapper” that encompasses various codecs (encoder/decoder-compressor/decompressor software), which define the size, rate and compression (if any) of that media file. As such, QuickTime can be used as an origination, destination or interim file format, depending on your needs. Any computer with the same installed codec can display, copy, convert and otherwise manipulate the file.
The Present State
All of these methods offer some great workflow opportunities, but for the time being, it is still best to stay within the same family of products for the most universal file interchange. If you offline edit on Final Cut Pro, online on a Final Cut Pro system, too. If you offline on an Avid, stay with an Avid Media Composer, Symphony or Avid|DS for your online.
There are some changes to look for, such as from Apple, who is using the XML programming language to open “hooks” for others to use in exporting project information. The folks at Automatic Duck are busy using this to make a path from Final Cut Pro to Quantel’s editing products. In the future, this will permit you to offline your HDTV movie using Final Cut Pro with DV media, but then conform the HD master using Quantel’s advanced eQ or iQ editing platforms – hopefully with a direct transfer of all effects and color-correction metadata from your Apple to the Quantel system.
Even with the advances of AAF, XML or something else, I’d be willing to bet that the thirty-year-old EDL standard still won’t go away anytime soon!
© 2003 Oliver Peters