17.9. Extracting Audio from Video iMovie is perfectly capable of stripping the audio portion of your footage apart from the video. All you have to do is click the video clip in question and then choose Advanced  Extract Audio. As shown in Figure 17-13, the recorded audio suddenly shows up in your first audio track as an independent audio clip; its pushpins indicate that it's been locked to the original video.  | Figure 17-13. Top: Highlight a camcorder clip and choose Advanced Extract Audio.
Middle: The camcorder audio appears as an independent clip, which you can manipulate exactly as though its any ordinary audio clip.
Bottom: You can create a reverb or echo effect by overlaying the same extracted audio several times. (The "soundwave" images have been turned off here for clarity.) | |
This command unleashes all kinds of useful new tricks that are impossible to achieve any other way: -
Make an echo . This is a cool one. Copy the extracted clip and paste it right back into the audio trackand then position it a few frames to the right of the original, as shown at bottom in Figure 17-13. Use the slider at the bottom of the Timeline Viewer to make it slightly quieter than the original. Repeat a couple more times, until you've got a realistic echo or reverb sound. -
Boost the audio . The Volume slider at the bottom of the Timeline Viewer is a terrific help in boosting feeble camcorder audio. It does, however, have its limit: it can't crank the volume more than 50 percent above the original level. Sometimes, even that's not enough to rescue a line of mumbled dialog, or the distant utterances of eighth -graders on the school stage 100 yards away. When all else fails, try this crazy technique: Copy the extracted clip and paste it right back on top of itself . iMovie now plays both audio tracks simultaneously , giving an enormous boost to the volume. In fact, you can stack two, three, four, or even more copies of the same clip on top of each other, all in the same spot, for even more volume boosting. Now, there's a pretty good reason the Volume slider doesn't go higher than 150%. As you magnify the sound, you also magnify the hiss, the crackle, and whatever other underlying sonic noise there may have been in the audio. When you try this pasting-on-top trick, you may run into that problem, too. Even so, for insiders who know this technique, many an important line of dialog has been saved from oblivion. -
Reuse the sound . You can copy and paste the extracted audio elsewhere in the movie. (You've probably seen this technique used in dozens of Hollywood movies: About 15 minutes before the end of the movie, the main character, lying beaten and defeated in an alley, suddenly pieces together the solution to the central plot mystery, as snippets of dialog we've already heard in the movie float through his brain, finally adding up.) -
Crop the scene's audio . Trim out an unfortunate cough, belch, or background car honk by cropping the audio. Now the video can begin (or end) in silence, with the audio kicking in (or out) only when required. (Of course, complete silence isn't generally what you want either, as described next .) -
Grab some ambient sound . In real movie-editing suites, it happens all the time: A perfect take is ruined by the sound of a passing bus just during the tender kiss momentand you don't discover it until you're in the editing room, long after the actors and crew have moved on to other projects. You can eliminate the final seconds of sound from the scene by cropping or splitting the clip, of course. But that won't result in a satisfying solution; now you'll have three seconds of silence during the kiss. The real world isn't truly silent, even when there's no talking. The air is always filled with ambient sound , such as breezes, distant traffic, the hum of fluorescent lights, and so on. Even inside in a perfectly still room, there's room tone . When you want to replace a portion of the audio track with "silence," what you usually want, in fact, is to replace it with ambient sound. Professionals always record about 30 seconds of room tone or ambient sound just so that they'll have material to use in case of emergency. You may not need to go to that extreme; you may well be able to grab some sound from a different part of the same shot. The point is that by importing that few seconds of scene into iMovie, extracting the audio, and then deleting the leftover video clip, you've got yourself a useful piece of ambient-sound "footage" that you can use to patch over unwanted portions of the originally recorded audio. -
Add narration . The technique described on Section 17.2.1 is ideal for narration that you record at one sitting in a quiet room. But you can add narration via camcorder, too. Just record yourself speaking, import the footage into iMovie, extract the audio, and then throw away the video. You might want to do this if you're editing on a mike-less Mac, or if you want the new narration to better match the camcorder's original sound. It's important to note that iMovie never actually removes the audio from a video clip. You'll never be placed into the frantic situation of wishing that you'd never done the extraction at all, unable to sync the audio and video together again (which sometimes happens in "more powerful" video-editing programs). Instead, iMovie places a copy of the audio into the audio track. The original video clip actually retains its original audiobut iMovie sets its volume slider to zero, thereby muting it. As a result, you can extract audio from the same clip over and over again, if you like. iMovie simply spins out another copy of the audio each time. (When you extract audio, the video clip, too, sprouts a pushpin, but don't let that fool you. It's perfectly legal to extract the audio again.) If you intend to use the extracted audio elsewhere in the movie without silencing the original clip, no problem. Just click the video clip and then drag the volume pop-up menu back up to 100% once again. |
