Captioning - The instantaneous translation of the spoken language translated into text and merged with a video signal for broadcast or projection with less than a two-second delay. For example, the captioner's software dials via a phone line into the television station's encoder. The captioner then dials via a second phone line into an audio source at the television station. The captioner listens to the audio and transcribes what is heard.
This service is also used in large meeting sites and in convention settings. This service is known as "speaker image captioning."
Captioning services can be provided onsite or remotely. Closed captions are captions that can only be seen with a device called a "decoder," which is built into most televisions.
Open captions are captions that can be seen all the time. The caption text becomes part of the video signal.