Local insertion

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In broadcasting, local insertion (known in the United Kingdom as an opt-out) is the act or capability of a broadcast television station, radio station or cable system to insert or replace part of a network feed with content unique to the local station or system. Most often this is a station identification (required by the broadcasting authority such as the U.S. Federal Communications Commission), but is also commonly used for television or radio advertisements, or a weather or traffic report. A digital on-screen graphic ("dog" or "bug"), commonly a translucent watermark, may also be keyed (superimposed) with a television station ID over the network feed using a character generator using genlock. In cases where individual broadcast stations carry programs separate from those shown on the main network, this is known as regional variation (in the United Kingdom) or an opt-out (in Canada and the United States).

Automated local insertion used to be triggered with in-band signaling, such as DTMF tones or sub-audible sounds (such as 25 Hz), but is now done with out-of-band signaling, such as analog signal subcarriers via communications satellite, or now more commonly via digital signals; broadcast automation equipment can then handle these automatically.^{[citation needed]} In an emergency, such as severe weather, local insertion may also occur instantly through command from another network or other source (such as the Emergency Alert System or First Warning). In this case, the most urgent warning messages may interrupt without delay, while others may be worked into a normal break in programming within 15 minutes of their initial issuance.^{[citation needed]}