Indeed--it was more of a hack sixty years ago perhaps. Since then, similar tricks have been used for closed captions, Dolby surround (the original kind), Radio

Indeed--it was more of a hack sixty years ago perhaps. Since then, similar tricks have been used for closed captions, Dolby surround (the original kind), Radio Data System (which puts song names on your car dashboard via FM radio), TV Second Audio Program (listen to shows dubbed in a second language, just press the SAP button on your ancient high-end TV!)....