April 2, 2006
By Clay Coleman
If you haven't been confronted with it previously,
.BWF (Broadcast Wave Format) is an audio format initially
developed under the auspices of the European Broadcast Union
around 1996 as a non-proprietary 24 Bit Integer audio file format.
The original intent was to provide broadcasters within the EBU
with a simple, high-quality, tapeless digital audio platform
to streamline workflows for the member countries. Since adding
TimeCode and MetaData functionality in 2000, it has become a
widely-used format for hard-disk digital audio recording for
radio, television and film. Using a BWF recorder, like the Sound Devices 744T, and a simple file conversion
tool, the BWF2XML file converter, BWF allows for extemely fast
audio capture in excellent quality with multiple tracks simultaneously,
and while retaining original timecode and filenames for later
synch to picture and audio post workflows.
Interesting thing is, BWF was made QuickTime compatible somewhere around 2002, but for whatever reason, that fact never made it into the FCP or QuickTime documentation. BWF audio is still not mentioned in the FCP Studio manual (as of 2006), and that is something Apple should definetly change in future versions. In fact, if you had a version update request something along the lines of "hey, how about giving us really good digital audio with instant multi-track import and with original timecode, and in PAL, NTSC, and 24, and how about with a simple way to maintain shot, scene and take numbers, and please make the workflow completely tapeless, etc., etc.", well, wait no longer. It already exists. Those in the know have been using BWF for some time now. I came across it recently when a recordist on a recent job sent me his workflow specs. After then posting a query on the lafcpug forum, I was clued in pretty quickly. The rest was a bit of research, a few tests, and then using it on the current job. Thus the impetus for this beginner's how 2, and in hopes that BWF audio comes into much wider use, because it's an editor's dream.
The Gear:
This is the Sound Devices 744T deck, as was used during shooting. Up to four tracks of BWF audio can be recorded to it's internal 40 GB drive simultaneously. How much audio (in hours and minutes) you can get onto the drive of course depends on the settings used. The chart below from the Sound Devices homepage gives you the general idea of storage requirements for one track of audio at the various settings availalbe. For example, recording at 24 Bit / 48K, the 744T would allow you about 20 hours of 4-Track audio. More than ample for a day's shooting.
On the 744T's right side panel, you'll notice the Firewire 400 port. It's both Mac and PC compatible (OSX), and allows connection directly to your computer. The 744T's internal disk mounts as an external drive on the desktop, letting you copy BWF files straight from the deck to your media drive.
For editors though, one of this deck's handiest features is the ability to enter individual filenames of up to 9 Digits. For example, we opted for a standard scence, shot and take number routine, thus allowing for filenames like 03-07a-5 (Scene 3, Shot 7a, Take 5) as per the director's breakdown, and as subsequently slated. Once set, those filenames are maintained from recording all the way through edit and post. A major time-saver, streamlining the otherwise tedious job of logging and capturing audio down to a few mouse-clicks.
Getting .BWF Files in:
Step one in importing and converting .BWF audio is to get the orignal files copied to a designated media drive on your machine. As above, you can pull it right off the deck via Firewire, but in most workflows, you won't have (or even need) the deck in the edit bay to import from. More likely, you'll get the material from the audio dept in the .BWF file format. In this particulart case, I was given a Data DVD with all the audio files, so bringing it in was just a matter of drag and drop. Folders were created for each shoot day, a procedure to retain as will become evident, and saved to the project's media drive. Popping open a folder as below, you'll see the individual file names appear with the.BWF suffix, file size, and date modified info. As advertised, each audio take is displayed as the recordist named it during shooting by scene, shot and take numbers.
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Original folders:
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Sample contents:
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Converting and Saving the Files via BWF2XML:
Step 2: to start the conversion process, you need to purchase and install the BWF2XML tool. Details on how to do that are at the end of this article. Once in your applications folder, the converter icon shows up as below. Double-click to launch.
You then get the BWF conversion dialog window:
At this point there are 2 choices, either hit the Load BWF bar to proceed with the conversion at the current settings, or go into preferences to fine tune things. Prefs are accessed by simply clicking in the text area (which opens an additional preferences pane) and by heading up to the menu bar and adjusting further settings there.
A number of very useful features are available, including being able to generate a log file. A 12 channel audio mixer let's you make volume and pan adjustments prior to conversion. (Hang on, twelve channels? Yes, but for the moment, just to keep things simple, I'm sticking with up to 4. More on multichannel towards the end of this piece.) Video frame rates of 23.98, 24, 25, 29.97 and 30 fps are supported, as well as the more exotic 29.97 DF vs. NDF issues which can arise when synching 29.97 audio to telecine. A word on that later too.
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It would take too long to go into all the details of each setting here, but suffice it to say that after testing the main functions, everything works as it should, and the Help documentation is simple and straightforward. To convert the files at hand, I set the timecode to 25 (my timebase is DVCProHD/1080i50), hit the "Load BWF" bar, set a destination folder, and started a batch conversion of each shoot day's files (yes, you have the option of grabbing individual files or an entire batch). The converted files in one of the new folders (each folder was named BWF Conv plus date), look like this:
The first thing you'll notice is the very small and continuous (4KB) file-size displayed for each take. That is because although they are defined as FinalCutPro Movie Files, they are actually links between the BWF format and QuickTime via an XML file that is generated during conversion. The XML file enables retention of each files' MetaData, keeps the tracks separate, and an XML file for each conversion is saved to the destination folder.
Important: this is where you've got to exercise some caution, because once converted, these file links can now be imported into FCP and edited and played back just like any other audio files, but, they can't be moved from the their current location without potentially becoming corrupted. They also can't be copied to a different drive for the same reason. However, there is an easy fix to that problem, which I'll get to in a second.
Importing into FCP:
Step 3: to get the converted audio into FCP, just import files or a folder as required in the usual manner. In the FCP browser, each file shows up with the original scene, shot and take number, with the original timecode, and displaying how many tracks each file includes:
As to be expected, when opening a clip in the viewer and with the playhead set at the head as below, you then see each track within the clip, the audio waveforms, duration, original timecode and original filename. Very, very cool.
From there, it's just a matter of getting onto the timeline to synch to picture. In this case we did it the old way, lining up slates with waveform peaks. If you have timecode from camera into the BWF recorder (which the 744T can do), then of course you'd have the added luxury of simply lining it up by TC. Here's a few 4-Track clips, recorded with various boom and radio mics, after editing into the timeline for synch to slates:
Backing Up to QuickTime:
The only other thing you really should do is Batch Export those converted files from the browser as QuickTime .mov files with Audio Only. Edit with those, and keep the original .BWF's and the 4KB converted files as backup. You can then move the new QT .mov files around to other drives if need be without them becoming corrupted. And yes, the exports do retain all the separate tracks, the original filenames, and the original TC, so there's no reason not to take the safe route.
At this point you're probably wondering what happens if you open a .BWF file with QuickTime or Compressor without doing the conversion. QuickTime is .BWF compatible, so you can hear the audio in the QT player, and you can export to .mov or .aiff. Only thing is, it's then maximum 2-Track and you lose the original TC. If you import a .BWF file into FCP directly, it will display all the tracks and you can playback and edit the clip, but again, the original TC is gone, and any attempts to export starts creating a lot of error messages. Therefore, the BWF2XML tool is essential to making the workflow run smoothly and with all functionality fully operative.
Bottom Line:
And that's basically it. Although the workflow via XML and then to QuickTime involves an extra step or two, the conversion goes so quickly that it doesn't really matter. In this case, audio from a four day studio shoot amounted to just over 300 takes, or about 3.2GB. The initial conversion via the BWF2XML tool went off within two minutes. Importing into FCP and then Batch Export to QuickTime took about 4 minutes on a dual 2.5 G5. Not an issue, especially when compared to capturing DAT audio real-time, or having to make second passes of camera audio in real-time to get all the tracks, plus the logging hassle. A bit of good file organization is all that is otherwise required.
Another added benefit of backing up to QuickTime from the converted files, is that one can of course send the audio to a Soundtrack multitrack project, or export to .omf for further sweetening and mix at an audio facility. There are numerous very good reasons for using external audio both for film and video, the main one being that the camera is often nowhere near where mics want to be, thus involving extra cables and gear hanging off the camera for people to stumble over and fumble with, which DP's generally despise. The recording quality depends largely of course on the skill of the recordist and the mics used, but in the hands of a competent person, .BWF is an excellent low-cost high-end solution. Also for the editor, who, with literally just a few mouse clicks, is spending less time on the drudgery of log and capture and more time on the important part.
The Bigger Picture:
As regards 5.1 and 7.1 recording, editing, and mixing is concerned, .BWF is already in use in that arena too, and that's the reason why the conversion tool currently has a 12 channel mixer on board. A .BWF file can contain 12 or more tracks of 24 Bit audio. Theoretically, the number of tracks is unlimited. It's currently a hardware issue to handle that much throughput to disk, but the format can already deal with it. On a multi-camera shoot, 12 or more channels of audio is not uncommon. In the future, we'll be seeing machines that can record multiple tracks, while saving to one multi-channel .BWF file. Therefore, although video has taken the limelight recently with the jump to HD, the audio world has not been asleep at the switch. Far from it. Great new possiblities are already here with more to come in the very near term.
The .BWF file format is certainly something FCP users need to at least know about. Imagine working in DVCProHD on P2 with .BWF 24 Bit external audio. No tape, no decks, modest file sizes, no expensive storage solutions, excellent qualtiy, and instant compatibilty with all the FCP Studio apps. A true tapeless post solution. Let's get all that into the FCP Studio Manual.
Contributors:
Many thanks to Andreas Kiel at Spherico.com, the rocket scientist who developed the BWF2XML tool. Available for $95 in the lafcpug store, it's very fairly priced, especially when you consider the time-savings involved. Andreas also provides support for various film and video workflow solutions, and is experienced in dealing with longform projects as well. Should you get stuck with 29.97 DF/NDF audio synch to telecine problems, the converter can handle it. Andreas can tell you how. Contact him directly too for any customizing needs.
Thanks also to David Urban, the recordist on this job, who gave me a few test files to play around with prior to shoot, then generally explained how it all works and took me through the converson procedure first time around. Very helpful.
Further thanks to Jon Tatooles, one of the founders at Sound Devices. Their 744T is a great piece of gear, very innovative, easy to get into, very robustly built for field use, and thus highly recommended. The ability to enter scene, shot and take numbers as individual filenames, and thus retain that information all the way through post, is an excellent feature.
Resources:
Want more tech? The following links will get you started:
The European Broadcast Union's .BWF spec
page with Userguide and FAQ:
www.ebu.ch/en/technical/publications/userguides/bwf_user_guide.php
Sound Devices Homepage with Gear, Descriptions,
Specs, and PDF's
www.sounddevices.com
The BWF2XML conversion tool Developer's
Homepage:
www.spherico.com
Hope this helps,
Clay Coleman
Oasys Editing
Munich
All images used by permission. / © 2006 Clay Coleman
Clay
Coleman is a free-lance FCP editor since version 2.0. Oasys
Editing is his home base in Munich. Projects there include work
for TV, Corporates, Short Features, and Docus. Clay also teaches
DV filmmaking at Munich's Graphic Arts Akademie U5.
