A virtual source is a clip consisting of a single frame that behaves as if it were repeated indefinitely. When edited into the timeline, it can be trimmed, slipped, or slid to any extent—the virtual source automatically generates new frames on an as-needed basis. Head and tail frame counts are usually numeric, but because virtual sources have unlimited heads and tails, these are indicated by an asterisk (“*”).

You can create a virtual source in any of the following ways:

• Using the Colour Source command in the A/V Tools menu. (The Noise and Colour Noise frame types do not produce virtual sources because each frame is distinct.)
• Using the Repeat command, with the Frame option, in the A/V Tools menu.
• By creating a single-frame clip in any tool or module.
• When importing a still image (with or without the Repeat option).

To view information about a virtual source clip, zoom in on the timeline or Alt-click the timeline element.