What can you use to create a window of visibility?

Using a track matte is a powerful technique for creating a window of visibility in Adobe After Effects. When you apply a track matte to a layer, it determines which areas of that layer will be visible based on the transparency of another layer. This is particularly useful for creating effects where you want to reveal or hide portions of a layer based on the content of another layer, effectively acting as a mask that controls visibility.

For example, if you have a video layer and you place a shape layer above it with a fill, applying the shape layer as a track matte will allow the video to only show through the areas covered by the shape. This means that the shape acts as a sort of 'window,' showing the underlying content only through its contours.

While the other options serve different purposes, they do not create a visibility window in the same way. Layer masks are focused on controlling visibility directly on the layer to which they are applied, adjustment layers affect effects or properties but do not control visibility directly, and solid layers can serve to block or blend, but cannot create a visibility window in the form of a matte without additional techniques.