XO Wave: Editing Sound for Video and Film

XO Wave is not only a powerful package for creating CDs and other audio content, it is also a great way to edit audio for video. In audio for video, or "sound for picture" applications, XO Wave allows you to manipulate audio while staying synchronized with your video. This has a range of uses, from soundtrack production to dialogue editing for TV, film, or "vodcasting" (video podcasting). This page gives a short introduction to the features of XO Wave that you'll need to understand in order to work on sound for picture projects. This page applies to XO Wave Free, Pro and Open, except that only XO Wave Pro can export QuickTime, and XO Wave Open only supports synchronizing to a limited set of video formats. In addition, if you are using XO Wave Open, it is best to use a video file with no audio track.

If you are new to XO Wave, you should probably read our CD Mastering Guide first, as this covers basic XO Wave techniques. If you are new to sound editing in general, you may also want to check out our Sound Editing Tutorial, which will give you an idea of how sound is displayed and edited in XO Wave. If you are having performance trouble or are choosing a video format to work with, you may want to read our Optimizing Mac OS X Performance for Audio and Video Users.

Adding Video to a Session

After creating or opening a session in XO Wave, you can associate a video file with it by selecting File:Movie:Open Movie. In the window, simply navigate to the file you want and select Open. The movie file will be associated with the session, and you'll see the video in the Toolbar of the Edit window as well as the Movie window. As you move around the session, the movie will jump along with you and when you play back, the movie will roll right along with your audio. XO Wave can read anything that QuickTime can read, which may include some surprises such as Flash and PowerPoint presentations, but it is really designed for video such as .mov, .avi and .mp4 (MPEG-4) files.

If you are working with a large project, you may want to use a smaller version of the video, so that it won't slow your CPU down during playback. When doing so, it's usually a good idea to reduce the resolution (width and height in pixels) rather than reducing the frame rate. This is because most audio for video applications require frame-accurate synchronization, which can only be done if you preserve the frame rate of the video. Of course, if you are working on a fast computer with a good video card, you may be able to work with full resolution video without any trouble.

If you have an audio track in the video file, it won't play back with the video, so you'll probably want to import it. To do so, import the movie as you would an audio file: drag the movie file into the Edit Area of the Edit window or select File:Import Audio. Once the audio is imported, you can put it on its own track by dragging it from the Region Bin into the New Track Area. In order to re-synchronize the audio and video, just make sure that you drag the audio all the way to the start of the session.

Note: You can associate a video file with the session and import its audio in a single step, by selecting File:Movie:Open Movie and Import Audio...

Get Your Timecode Right!

When working with video, you'll usually want to use timecode, rather than, say, wall-clock or samples to measure time. In the Edit window, you can do this simply by selecting Time Code from the first pop-up in the Time section of the Toolbar.

Showing time in timecode is easy enough, but you need to make sure you are using the same type of timecode as the video. To change the timecode type, select Windows:Session Setup and select the timecode type your video uses. If you are unsure which timecode you are using on your project, check with your production manager or use these rules of thumb (for more details and an explanation of the terms, see our article All about Time Code):

• If you are working with color video from North America (NTSC), use 29 DF. Shorter projects such as commercials and music videos may use similar formats, such as 30 ND or 29 ND, but this is usually because the timecode formats are not correctly understood. If you are working on a project that calls for one of these timecodes, first make sure there isn't an error -- 29 DF tapes are often mis-labeled 30 DF. Assuming a non-standard time-code was used, the best advice is to try to match the time-code type rather than the frame rate, as the difference between 29 frames per second (which is actually shorthand for 29.97 frames per second) and 30 frames per second is smaller than the error when using drop frame in place of non-drop -- at least for short projects.
• If you are working with film, select 24 FPS.
• For European PAL/SECAM video, select 25 FPS.
• If you are using black and white video from North America, use 30 ND.
• When in doubt, open the file in QuickTime Player and select Movie Info from the Window menu. The Info window normally shows the actual frame rate of the video file, although this may or may not be the same as the frame rate of the project (for example, it may be a film project converted to NTSC video).

Fortunately, working on a computer with video files instead of an analog video player will shield you from having to be intimately familiar with all the details, but when in doubt, you should read our article All about Time Code.

Working with EDLs

As you start to work with an audio for video project, you will often find yourself needing to know exactly where a particular edit in the video happens or where audio for a particular clip is supposed to come from. An EDL ("Edit Decision List") is the place to find this information. An EDL lists each edit made to a video project, along with information such as the source of each video clip, and so on. If you are working on a project that involves a video with many edits, be sure to obtain an EDL so that you can refer to it when making your own edits. The actual format of the EDL will vary depending on the software used to edit the video but any reasonably professional editing package, such as Premiere, Final Cut Pro, or Avid, can output some form of EDL, usually as a simple text file that you can read and refer to for information such as take number for a given edit. Of course, an EDL, even a great one, is no substitute for the location logs, so make sure you have those too!

Synchronizing the Unsynchronized

It often happens with audio for video projects that the audio and video are not synchronized, either because they were recorded separately and no effort was made to synchronize them, or because the sound is being re-recorded because of poor or inadequate location sound. Audio is often recorded on one system, such as a DAT deck, while video is recorded on another, such as a film or digital video camera. Reconciling these sources requires planning and work, but it does not have to require a large expense: a good old fashioned film "clapper," or traditional slate (also called a "clapboard" or "clapperboard"), works well and is still a popular option to this day for budget film projects. It is far cheaper than renting a Time Code recorder and "smart-slate" and paying a production house to synchronize for you. But whether your unsynchronized audio comes from the set or from re-recording, here are some general tips and guidelines for synchronizing audio:

General Tips for Synchronizing in XO Wave:

To go through the video frame-by-frame, select Time Code from the top pop-up in the Time section of the Edit window, and Frames from the next pop-up. Click somewhere in the Edit area, and then use the J and K keys to move one frame at a time. To move one second at a time, just use Control-J and Control-K, and to move one sub-frame at a time, use Option-J and Option-K. If you have selected a region of audio, these commands will move the audio, too.

"Smart-Slate" Synchronization:

To synchronize audio to video using a digital "Smart-Slate", start rolling both the camera and the sound. The sound recorder (often a DAT machine or a portable hard-disk recorder) produces Time Code which gets displayed on a smart slate. The smart slate should be filmed by the camera so that later the film or video can be lined up with the audio. Usually the person holding the slate reads the slate contents (e.g., time and date, scene, take, and production information) out loud, and then gets out of the way so that the scene can begin. It is usually the video post-production house's job to re-synchronize time-coded audio tapes with the video or film.

"Clapper" Synchronization:

To synchronize audio to video using a clapper, or traditional slate, start the camera and sound rolling. Focus the camera on the slate and have the person holding the slate read its contents (e.g., time and date, scene, take, and production information) out loud. When they are done, they should say "mark" and drop the top part of the clapper so that it makes a loud noise. The scene can then carry on. To synchronize the audio and video later, simply align the sound of the clapper with the video frame where the clapper closes. Sometimes it is necessary to "tail-slate" the scene, (that is, to slate after the scene has been filmed), which is traditionally done with the slate held upside-down.

Synchronizing Multiple Audio Sources:

With the increasing quality and decreasing cost of video, many productions are moving to shooting on video, but still using separate systems for audio, because even the best video cameras have very poor support for professional audio requirements, such as pro (XLR) mike inputs and good mixer controls. The best thing to do in this case is to use the "clapper" or digital slate to synchronize the audio and video as you would with film. If there is some problem with the slate, you can use the waveforms of the audio from the video camera to line up the audio from the higher quality audio recorder. Lining up camera and "Pro" audio using the waveforms can be a bit tedious, but if everything is well documented (remember to get that EDL!) it can be made to work, and it can get you out of a jam. (I once edited an entire feature film this way because the video editing house forgot to synchronize the sound before editing!)

Synchronizing Re-recorded Sounds:

On many big productions, as much as 90% of the dialogue may replaced after filming. Most smaller productions need to do a little Foley, sound effect, and dialogue re-recording as well. The best thing to do here is use the location sound -- however bad it may be -- as a reference. Line up the peaks in waveforms of the original audio with peaks in the waveforms of the re-recorded audio and you'll usually get it right. If you don't have original audio, try to use the video. For example, if you are trying to create a hand-clapping sound, try to find the exact video frame where the hand-clapping happens, and then line up the peak in the audio file with that.

Completing Your Project

Once you've created a session, synchronized a video file, and edited your audio, it's easy to create a finished product: just select File:Export:Export to QuickTime Movie or File:Export:Export to Any QuickTime Type, and XO Wave will walk you through the process of creating a QuickTime or other format movie. To create an iPod video file, just select File:Export:Export to iPod Video File.

For some work, you may not need a video file output. For example, if you are producing a sound track for a movie, and there is other audio that someone else will combine with the video for you, you can just select File:Export:Export to AIFF/WAV and select the appropriate format.

--Bjorn Roche