EIA-608

EIA-608, also known as line 21 captions or CEA-608, is a standard used for displaying closed captioning on analog NTSC television broadcasts in the United States, Canada, and Mexico. Developed by the Electronic Industries Alliance (EIA), it allows text such as dialogue and sound effects to be shown on screen, helping people who are deaf or hard of hearing follow television programs. The system works by sending the caption data on a part of the TV signal that viewers don't normally see, called line 21 of the vertical blanking interval.

In addition to captions, the standard also supports extra information known as "Extended Data Services" (XDS), which can include details like program titles or instructions for recording shows. This is similar to features found in some European TV systems that use a different signal format.