Choosing Composition Settings
Because compositions describe how layers are arranged in space and time, you must define a composition's spatial attributes (such as its frame size and pixel aspect ratio) as well as its temporal aspects (such as its duration and frame rate). Composition settings allow you to specify these characteristics. You can also use the composition settings to specify attributes that aren't as fundamental, such as the resolution or quality of the Composition panel's display. You can change composition settings at any time.
A project usually contains several compositions, most of which are contained as layers (or nested) in a final composition. Although you can set the final composition's settings according to your output format (NTSC DV, for example), you may want to employ different settings (particularly for frame size and duration) for intermediate compositions.
The Composition Settings dialog box is divided into Basic and Advanced panels. The following sections focus on the Basic settings. Although setting a Comp's anchor point is discussed here, other advanced settings are addressed in later chapters, when they'll make more sense to you. And rest assured, you'll be reminded of the appropriate Comp setting whenever a task or technique calls for it.