DVD

DVD, or "digital veratile disc"/"digital video disc" was a video playback technology developed on Earth in the 1990s, and which became the dominant playback format for visual entertainment media in the first decade of the 21st century.

Billy Shipton, acting on instructions received from the Doctor decades earlier, entered into the DVD authoring business after plying his trade in video publishing. In the mid-2000s, he arranged surreptiously to have a specially encoded Easter egg file added to each of 14 commercially released DVDs. The file, when located by viewers, played a one-sided video message from the Doctor recorded in 1969 intended for Sally Sparrow. Ultimately, the message would be first noticed by Larry Nightingale (who worked in a DVD rental shop) and other Internet forum users, before finally being seen by Sparrow herself in the midst of her encounter with the Weeping Angels. Sparrow eventually realizes that the 14 DVDs containing the Easter egg consisted of her complete collection of DVDs at that time. The Easter egg file served an additional purpose; it transformed each encoded DVD into a special control disc good for a single one-way journey in the TARDIS. When inserted into a DVD drive mounted to the control console, the file activated the TARDIS and sent it back to 1969 to be retrieved by the Doctor. (DW: Blink)