AfterEffects

Convert a layer into a track matte

  1. Drag the layer that will be the track matte directly above the layer that will be the fill layer.
  2. Define transparency for the track matte by choosing one of the following options from the TrkMat menu for the fill layer:
    No Track Matte
    No transparency created; next layer above acts as a normal layer.

    Alpha Matte
    Opaque when alpha channel pixel value is 100%.

    Alpha Inverted Matte
    Opaque when alpha channel pixel value is 0%.

    Luma Matte
    Opaque when a pixel’s luminance value is 100%.

    Luma Inverted Matte
    Opaque when a pixel’s luminance value is 0%.

After Effects converts the next layer above into a track matte, turns off the video of the track matte layer, and adds a track matte icon  next to the track matte layer’s name in the Timeline panel. The Composition panel displays the fill layer viewed through the alpha channel of the matte layer.
Note: Although the video is turned off for the matte layer, you can still select the layer to reposition, scale, or rotate it. Select the layer in the Timeline panel, and then drag the center (indicated by a circle with an X) of the layer in the Composition panel.