Creating Layers
Layers are the elements that make up a composition. Without layers, a composition is just an empty frame. You can use any number of layers as needed to create your composition. Some compositions contain thousands of layers, and some contain just one layer.
Layers in After Effects are similar to tracks in Adobe Premiere Pro. The main difference is that each After Effects layer can contain no more than one video element as a source, while a Premiere Pro track usually contains multiple clips. Layers in After Effects are also similar to layers in Photoshop, although the interface for working with layers is different. Working with layers in the Timeline panel in After Effects is similar to working with layers in the Layer panel in Photoshop.
You can create several types of layers
Audio and video layers created from imported video elements, such as still images, movies, and audio tracks
Layers that are created in After Effects for special functions, such as cameras, light sources, adjustment layers, and blank objects
Solid color layers created in After Effects from solid color video elements
Synthetic layers that contain visual elements created in After Effects, such as shape layers and text layers
Pre-composition layers that use compositions as elements of the original video sequence
Changes to a layer do not affect the elements of its original video sequence. You can use the same video sequence element as a source for more than one layer, and use it differently in each instance. (See Importing and interpreting video sequence elements.)
Changes made to one layer do not affect other layers unless the layers are linked in some way. For example, you can move, rotate, and draw masks on one layer without affecting all the other layers in the composition.
After Effects automatically numbers all the layers in a composition. By default, these numbers appear in the Timeline panel next to the layer name. The number corresponds to the position of that layer in the overlay order. When you change the overlay order, After Effects changes all the numbers accordingly. The order in which layers are superimposed affects the rendering order, and therefore affects the rendering of the composition for preview and final output.
Layers in the Layer, Composition and Timeline panels
After you add a layer to a composition, you can change the location of the layer in the Composition panel. In the Timeline panel, you can change the duration, start time, and position of the layer in the layer order. You can also change the properties of a layer in the Timeline panel.
You can perform many actions, such as drawing a mask, both in the Composition panel and in the Layer panel. However, other tasks, such as motion tracking and coloring, should only be performed in the Layer panel.
Layer in the Layer panel appears before any transformations applied to the layer. For example, the Layer panel doesn’t show the result of scaling a layer. Use the Composition panel to view the layer in conjunction with other layers and with the results of transformations.
Layers that are not based on an element of the original video sequence are called synthetic layers. Synthetic layers contain text layers and shape layers. You cannot open a synthetic layer in the Layer panel. However, you can pre-assemble a synthetic layer and open a pre-composition in the Layer panel.
Opening Layers and Layer Sources
To open a layer (other than a pre-composition) in the Layer panel, double-click the desired layer, or select it and choose Layer > Open Layer.
To open the original composition of a pre-composition layer, in the Composition panel, double-click the desired layer, or select it and choose Layer > Open Composition.
To open a source video element, double-click the layer while holding down the ALT key (Windows) or the OPTION key (Mac OS), or select it and choose Layer > Open Layer Source.
To open a pre-composition layer in the Layer panel, double-click it while holding down the ALT key (Windows) or the OPTION key (Mac OS), or select it and choose Layer > Open Layer.
Creating Layers from Video Elements or Changing the Layer Source
You can create a layer from any video element in the Project panel, including from another composition. Once a video sequence element has been added to a composition, the created layer can be modified and animated.
When adding one composition to another, create a layer that uses the composition you added as its source.
The “Freeze Frame Video Story” setting (“Preferences” > “Import”) controls the default duration of the layers that use the still elements of the video sequence as sources. By default, when you create a layer whose source is a still image, the duration of the layer is the same as the duration of the composition. You can change the duration of a layer after it is created, using the clipping method.