In an iMovie project, sound often plays almost as important a part as video. Sound and music can set the stage for a romance, suspense , comedy , or thriller. It can help create pacing for the movie and smooth through otherwise troublesome video transitions. If you've been using iMovie to import and arrange movies from your camera, you've already got audio in your projects. Movie clips themselves can contain embedded sounds, and these are usually transferred and saved along with the movie files. While this is convenient if you only want to use the sounds you've recorded with your camera, it doesn't give you the flexibility to mix sounds or add additional sounds to your movie.
To accommodate additional sound effects, iMovie includes two sound tracks that can hold any sound, music, or audio that you'd like. Figure 16.10 shows the three available iMovie tracks ”Video/Audio, Audio Track 1, and Audio Track 2.
Figure 16.10. Audio can be part of a video track, or can be added to either of the two audio tracks.
There is no difference in functionality between the audio 1 and 2 tracks. You can use one track to hold sound effects, the other for background music, or mix and match them as you choose. In addition, each track can overlap audio clips ”allowing you almost limitless layers of audio. You could, for example, have a base piece of background music in audio track 1, then, perhaps an environment sound track layered on top of it, and, finally, sound effects layered on top of that in audio track 2. Figure 16.11 shows a layering possibility much like this scenario.
Figure 16.11. Audio can be layered via the different audio tracks, or within a single audio track.
Sounds that are added to either of the audio tracks can be moved to the other track by clicking and dragging between the tracks in the timeline. No matter what type of sound you're adding, it is referred to within iMovie as an "Audio Clip."
However you've decided to layer your audio, iMovie will automatically composite it correctly when you play back your movie project. If you've included audio clips in all of the tracks, they'll automatically all play back when you play the movie.
Sometimes this can get to be a bit of a pain as you try to fine-tune your special effect sounds and don't want to hear the dialog from your video tracks, or the background music you've added. To enable you to focus on a single set of audio, Apple has provided the ability to control audio playback using the three checkboxes to the right of the video and audio tracks, shown in Figure 16.12.
Figure 16.12. Turn on and off audio tracks to focus on a particular part of your sound editing.
You can also control the overall volume of the movie using the volume control slider to the right of the main playback controls.