Definitions for "Preroll"
To start a videotape and let it roll for a few second before it is put in the playback or record mode in order to give the electronic system time to stabilize. Often necessary for analog devices.
The process of rewinding videotapes to a predetermined cue point (for example, 6 seconds) so the tapes are stabilized and up to speed when they reach the selected edit point (during digitizing of source material from a video deck).
To capture or play a number of video frames or a portion of audio data before encoding or rendering begins, in order to allow the source device to stabilize. Also used as a noun to describe the portion of the data to be prerolled.
Keywords:  buffering, clip, seconds, occurs, start
Buffering that occurs at the start of a presentation. Preroll should be 15 seconds or less.
Buffering that occurs before a clip plays back. Preroll should be no more than 15 seconds.