Closed-Captioning, Online and Offline
Open Captioning

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Closed captions are captions that are hidden in the video signal and are invisible without a special decoder.  The place they are hidden is called Line 21 of the vertical blanking interval.  The Television Decoder Circuitry Act, which became effective in 1993, required that all television sets ( with picture tube of 13 inch or larger) sold in the U.S. must have  a caption decoder built into it.

 If you use your VCR to tape a program that is closed captioned, you can play the tape back with or without the captions whether or not they were apparent as you were taping by simply setting your TV to show captions, because they are hidden in Line 21 and will become apparent when you set the TV to use the decoder .

Open captions simply show.  No decoder required, and you can't not show them.  The captions are essentially burned into the media.  Why would open captions be preferred at times?  Well, our school, like many others, has a lot of older televisions and monitors that don't have decoders built into them.  To assure that the captions will be visible no matter which display unit is used, open captions can be used.

 Online captioning is done in what court reporters call realtime.  The captions are written  as they are heard, such as in a newscast or live event.  Court reporters have the skill to write at a rate of 225 words per minute or above.  
The captioning can be broadcast captioning or  realtime captioning. 

Realtime captioning refers to to a court reporter writing what is being heard, using a specialized software program to instantaneously translate the machine shorthand notes into English, and some sort of display device to show the text to an audience of one or thousands.  

When captioning software is used by a court reporter, typically three lines of text
“roll up” usually at the bottom of the screen.  The court reporter has the capability to move the captions about the screen so as not to cover up important visual material.  

Offline captioning is captioning done on a videotape.  This does not require a realtime stenocaptioner and some companies use typists at QWERTY keyboards to create a script to go with the video and then use time codes to insert the captions.  This can be done in the roll-up fashion,  pop-on or paint-on.  

Pop-on is generally preferred as the captions are easier to read.  Pop-on captions can be set to appear anywhere on the TV screen.  The most difficult thing to understand about this process is how time consuming it is.  It often takes well more than 10-15 hours to caption a one-hour videotape as the time codes and protocols must be carefully set and tested.  The captions must be synchronized with the video, placed, checked, formatted and applied to the video using an encoder.

Roll-up captions typically use three lines, often set at the bottom of the screen and the text scrolls up and then off the screen continuously.  This is what you see on live programming.  Watch your TV.  Notice how many of the commercials are prescripted and often have pop-on captions, but when you get back to the live programming, roll-up captioning will resume.  

Court reporters can also provide offline captioning with captioning software and roll-up captions.  The benefit to using this second method would most likely be cost savings and quality, especially in the educational arena.  The final product does not have pop-on captions but the process is completed in fewer hours. 

Open captioning is always apparent to the viewer and can’t be turned off.  The captions are burned into the picture.  No decoder is needed. 

“Subtitling” is the term used in the U.K.  

When addressing public audiences, open captioning meets ADA requirements.

Captioning Methods by Joe Clark  (SGML, subtitling, audio description and dubbing)

Open and Closed Captioning

Captioning - How it Works