Playback

Playback is the process of playing pre-recorded music, other sound or sometimes video while a scene is being recorded.

In 20th century Doctor Who
Sometimes, as was often the case in the 1963 version of Doctor Who, the piece being played back is retained in the final assembly of the scene. Playback was often used by Doctor Who directors in lieu of editing to insert model shots and sequences pre-recorded by vacationing actors into the virtually "as live" recordings of the Hartnell and Troughton eras. Playback was occasionally used later in the 1963 version of the programme to insert footage onto on-set video-screens. CSO effects were also sometimes done through playback, though most often chroma-key was composited from two scenes being recorded simultaneously. A major and consistent use of playback was with the title sequence. It was played into the actual recording of principal photography, rather than edited onto the start of the episode during post-production. In other words, viewers never saw an actual first generation copy of the title sequence, but a recording of a playback from the master. This caused slight variations in the title sequence from week to week. These were most noticeable on Colin Baker episodes because of the intricate optical processes and huge variations of colour employed in that particular sequence. Co-creator Sid Sutton has said: "Some weeks it looked great, just as you'd produced it, and some weeks it looked . . . a little bit iffy." (DOC: The Star Man) This artefact of playback is less detectable on 2|entertain DVDs due to the restoration process.

In BBC Wales Doctor Who
In the BBC Wales era of the programme "playback" more often refers to the introduction of pre-recorded material that will not be preserved in the final edit of the scene. For instance, director Toby Haynes played back a musical cue from  while recording a scene from The Pandorica Opens to better guide his actors' movements. This music was then removed from the soundtrack of Pandorica, leaving his actors invisibly paced to a certain tempo. (CON: "Alien Abduction")