Tally light

In a television studio, a tally light (or on air indicator) is a small signal lamp on a professional video camera or monitor.

This is also the case when multiple cameras are placed in rectangles on screen, sometimes referred to as picture-in-picture (PiP) mode.

The ISO content is typically used for B-roll shots, such as people's reactions when it's uncertain if, when, and how they will react.

The common interfaces are SDI, Ethernet, USB, and HDMI (the latter's main role is outputting the video signal, but it can also accept a number of control commands).

In some (mainly non-studio) cameras, the tally light is implemented as a special UI element displayed on the screen (e.g. red outline around the frame).