Use alpha channels

Alpha channels provide an easy way to composite one image over another. Using an application like Motion, an Apple application designed to work with Final Cut Pro, you can create still images and video clips that have alpha channels. Alpha channels can be thought of as having a built-in keyer—when you use the key effects you are creating a mask that is used in the same way a clip with an alpha channel is used for compositing.

Below is an example of a clip with an alpha channel, showing the image that fills the alpha channel.

Viewer showing alpha channel fill image

Below is the alpha channel image—the white areas define the video areas that are composited over the background. The gray areas (which define the shadow in this example) define parts of the image that are partially transparent.

Viewer showing alpha channel matte image

This is what the final composite looks like over a background clip.

Viewer showing alpha channel clip composited over background clip

Use a clip with an alpha channel

  1. Position the playhead in the Timeline where you want to add the alpha channel clip.

  2. Select the clip that has an alpha channel in the Browser, and choose Edit > Connect to Primary Storyline (or press Q).

  3. To see the composited clips, position the playhead within the clip that was just added above the primary storyline.

    Timeline showing alpha image clip connected to background clip

The clip is composited over the primary storyline video clip, with the alpha channel controlling the opacity of its clip.

You can also use the Opacity adjustment’s fade handles to dissolve the foreground clip on and off.