In Canada, parliamentary and public affairs channel CPAC similarly uses SAP to carry both English and French-language audio.
Under the Twenty-First Century Communications and Video Accessibility Act of 2010, top U.S. television networks and cable networks have been gradually required to broadcast quotas of audio described programming per-quarter,[1][2][3][4] Since May 26, 2015, broadcasters have been required under the Act to provide dictations on SAP of any "emergency information" displayed in a textual format outside of the Emergency Alert System and newscasts.
[5][6][7] MTS features, including stereo and SAP, travel on subcarriers of the video carrier, much like color for television.
These travel the same way as the discrete left and right main audio channels, and ATIS station ID, which is heard as Morse code.
HD Radio subchannels, somewhat more widely available, operate on a similar premise but generally carry totally unrelated programming to the main feed.