It consists of a video stream playing within an inset window, freeing the rest of the screen for other tasks.
For televisions, picture-in-picture requires two independent tuners or signal sources to supply the large and the small picture.
A separate video or RF input was available on the back of the set and displayed in black and white on one of the four corners of the screen.
The Blu-ray Disc and HD DVD specifications included picture-in-picture, allowing viewers to see content such as the director's commentary on a film they are watching.
Some web browsers (including Google Chrome, Firefox, and Safari) provide APIs or similar functions that allow a playing video to be opened in a pop-up overlay atop other applications.