Following Action with Traveling Mattes

Keep your previous project in the timeline. You'll need it in a moment.

Select a clip that has something moving around in it?for instance, a racecar coming out of a turn and down the straightaway, someone walking down a street, or an aerobatic plane doing loops. As with the previous task, place the clip on both Video 1 and Video 2, either ahead of your previous project (automatically sliding it to the right) or after it.

Give the clip on Video 2 a distinctive look, like the effect you created in the first task. You can choose to apply one or more video effects or you can borrow what you came up with earlier (see tip).

To reuse an effect applied to a different clip: Right/Option-click the clip with the effect. Select Copy. Right/Option-click the clip you want to apply the effect to and select Paste Attributes. To apply the effects globally to all the clips on a track, use the Track Select tool to select a track and then select Edit, Paste Attributes. As illustrated in Figure 16.8, this opens a dialog box. You can select Content or Settings. Content deals with in- and out-points. Figure 16.8. The Paste Attributes dialog box lets you duplicate effects applied to other clips. Choose Settings and, in this case, select only Filters and Fade Control. You're going to use a different transparency setting?Track Matte instead of Image Matte?and there are no motion settings to transfer. Click Paste. Check how it worked by opening the Transparency Settings dialog box for your action clip and expanding the video track to see the opacity rubberband. You may note that the fade control (the opacity rubberband) doesn't exactly duplicate what you created in the first task. Unless the two clip lengths match exactly, the handles will fall in different locations. That's OK. You'll just slide them to the correct spots later.

Create a matte with a square black box (if you want to skip that Reverse Key thing, create a white box on a black background). The box should take up about the size of the object you want to highlight. No need to be precise. You'll use the Motion Settings dialog box to fine-tune it.

Just for a change of pace, in this exercise you may not want to use the Reverse Key box. Leaving it off means most of the screen will take on the video effect you applied to the clip on Track 2. Only the track matte box, which is going to follow the onscreen action, will have normal color. This, too, can be an excellent, eye-catching effect.

Import your matte to your project and drag it to Video 3. Extend it to match the length of your action clip.

Open the Transparency Settings dialog box for the clip on Video 2 and select Track Matte. If needed, click Reverse Key and preview your effect. As shown in Figure 16.9, there should be a box displaying your effect in the Sample screen.

The purpose here is to have the box follow the onscreen action. Open the Motion Settings dialog box for the track matte on Video 3. Make sure Show All and Alpha: Use Clip's are checked.

This is where things get a little tricky. You need to play and pause the clip in the preview window. With each pause, click the timeline to create a new handle. That puts a little highlight on the new handle in the Motion Path window to help you locate it.

Drag that new handle to center the track matte box over the object in motion. Do that until you have enough points to create a smooth path. As shown in Figure 16.10, I needed six handles in addition to the start- and endpoints to define a smooth path.

As the object moves through the frame, it probably changes size relative to the track matte box. You may need to gradually increase or decrease that box's area. Do that by clicking each handle within the timeline and changing the zoom percentage to adjust the box size. I've highlighted this in Figure 16.10. I changed mine from 50% to 130% over the duration of the clip.