Compositing clips

Each video track in a Timeline panel contains an alpha channel that stores transparency information. All video track frames are completely transparent except where you’ve added opaque content such as video, still images, or titles. You can make areas of opaque content partially or completely transparent by adjusting a clip’s alpha channel or applying a matte or key to a clip. Clips on upper tracks cover clips on lower tracks except where alpha channels indicate transparency. Adobe Premiere Pro composites clips from the lowest track up, and the final video frame is a composite of clips on all visible tracks. Areas where all tracks are empty or transparent appear black. If necessary, you can use the File > Interpret Footage command to change how Adobe Premiere Pro interprets a clip’s alpha channel throughout a project.

Keep the following guidelines in mind when compositing clips and tracks:

If you want to apply the same amount of transparency to an entire clip, simply adjust the clip’s opacity in the Effect Controls panel.
It’s often most efficient to import a source file already containing an alpha channel defining the areas that you want to be transparent. Because the transparency information is stored with the file, Adobe Premiere Pro preserves and displays the clip with its transparency in all sequences where you use the file as a clip.
If a clip’s source file doesn’t contain an alpha channel, you must manually apply transparency to individual clip instances where you want transparency. You can apply transparency to a video clip in a sequence by adjusting clip opacity or by applying effects.
Applications such as Adobe After Effects, Adobe Photoshop, and Adobe Illustrator can save clips with their original alpha channels, or add alpha channels, when the file is saved to a format that supports an alpha channel. In these applications, you can display a checkerboard pattern that indicates transparency so that you can distinguish transparent areas from opaque white areas.