The segment between two clips in a movie is called the transition. You can use different transitions to smooth the flow from one clip into the next so that your series of individual clips doesn't look like a series of clips, but rather a movie that flows smoothly from one scene to the next. All video uses transitions of one sort or another.
The three most common types of transitions are the Straight Cut, Cross Dissolve, and Fade To or From Black. The straight cut isn't a transition that you have to apply; this is what happens when you don't add a transition. A Straight Cut transition occurs when one scene runs right into another. As long as the adjacent scenes are similar enough, the straight cut seems very natural and you don't even notice it. The cross dissolve is also very common. One scene dissolves into the next. This transition can be useful when the adjacent scenes are somewhat similar, but different enough that a straight cut is a bit jarring. The Fade To or From Black is one of the more useful transitions. With the fade, one scene fades to black or fades in from a black screen.
iMovie enables you to add a variety of transition effects to your movies with a simple drag and drop.
To get started, open the Transitions palette by clicking the Transitions button. The Transitions palette pops up and you see the Transitions tools (see Figure 18.8).
You can preview a transition by clicking it on the transition list. In the Preview window at the top of the Transitions palette, you see the transition applied to the clip you have selected; if you don't have a clip selected, you see that transition applied to the first clip in your movie. When you click Preview, you see a preview of the transition applied to the clip shown in the Monitor window. Because the transition will be applied to the end of the clip, place the Playhead there before you select the transition you are going to apply.
You can control the amount of time over which the transition effect is displayed using the Speed slider, which is just above the transition list. Moving the slider to the left makes the transition last a shorter amount of time. Moving it to the right stretches the transition out so that it takes longer to play. After you release the slider, you immediately see the transition in the Preview window. In the lower-right corner of the Preview window, you can see how long the selected transition takes with the current setting.
Applying a transition can be done in just a few steps, as the following example of applying a cross dissolve shows.
In the Clip Viewer, select the clip after which you want the Cross Dissolve transition to appear and move the Playhead to the end of the clip.
Click Cross Dissolve to choose it and then watch the preview in the Preview window.
Set its duration with the slider; try placing the slider in the middle of its range. If that is too long or too short, use the slider to set the proper amount of time for the transition.
When the timing looks close, click Preview to see how it looks on the Monitor.
After you are satisfied with the transition, drag the transition from the Transitions palette to the Clip Viewer and drop it between the two clips you want to transition between. The transition appears as a green box with arrowheads that indicate the direction of the transition (see Figure 18.9).
Transitions are fairly sophisticated effects and they require your Mac to do a lot of work to apply them to a clip. This process is called rendering. When your Mac renders a clip, it applies the proper amount of transition effect to each frame of the affected section of the clip. When you apply a complex transition with a long duration, this can take a while. Fortunately, you can continue to work while your Mac renders transition effects.
When you place a transition on the Clip Viewer, your Mac immediately begins to render it; you see the small rendering progress bar at the bottom of the transition clip (seen in Figure 18.9). When the rendering process is complete, the progress bar disappears. While a transition is being rendered, you can preview the transition or you can move on to something else.
If you want to make adjustments to the transition, select it in the Clip Viewer and use the time slider on the palette to change its duration or use one of the transition's other controls to adjust it. Click Update to apply the change to the transition. (The clip will be rendered again.)
Continue adding transitions until you have made your movie really flow. At the least, add a Fade In at the beginning and a Fade Out at the end.
You can place two transitions adjacent to one another. For example, to have one clip fade out and then the next fade in, place a Fade Out and a Fade In between two clips.
Don't feel as though you need to have a transition before and after every clip. Sometimes the default straight cut works just fine. This is where your creativity comes in, so experiment until you achieve an outcome that is pleasing to you.
After you have your transitions in place, you see the new movie timeline in the Clip Viewer. Use the movement and editing techniques to watch your movie. Modify any of the transitions you aren't satisfied with.
You can play only portions of your movie by selecting the clips you want to play in the Clip Viewer (including transitions). When you press the Play button (or the spacebar), only the selected parts of your movie play. This saves time and helps you focus on particular parts of your movie. To play the whole movie again, deselect all the clips by pressing +D.