How are captions encoded onto standard definition tapes?
Standard Definition (SD) captions, also called 608 captions or line 21, are part of the video signal. They are a series of white pulses on line 21. For CC1 and CC2, they are in field 1. For CC3 and CC4, they are in field 2. The process of inserting these pulses into the video signal is called encoding. Most commonly, one sends video through an SD closed captioning encoder and records the output on another deck. This can be done at CaptionMax or at some post houses.
