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Information about captioning for video professionals

Volume 3 - Closed Captioning: The State of the Art

Television receiver technology has undergone major improvements in the past decade. Picture-in-picture, stereo surround sound with Separate Audio Program, 16:9 aspect ratio, new signal sources, improved picture quality and expanded channel capacity are just a few examples. Now, thanks in large part to the Television Decoder Circuitry Act of 1990, TV receivers and VCRs are taking another leap forward in sophistication. The closed-caption decoder mandated by the Act for most TV receivers is just the beginning. On the near horizon are a host of other new features that the built-in decoder makes possible.
A New Look for Captioning
The 1990 decoder law charged the Federal Communications Commission with setting technical specifications for TV receiver manufacturers. In the process, the FCC added new features to the decoder to improve the look and flexibility of closed captioning. For example, previously, captions could appear only in the upper or lower third of the TV picture; the FCC removed that limitation so that captions can be positioned anywhere on the screen. Real-time, or live, captioning, once confined to scrolling text in the lower third of the picture, can now be moved to other parts of the screen to avoid obscuring supers or important play in sporting events.
Following the FCC's action, the Electronic Industries Association (EIA, the trade group representing consumer electronics manufacturers) defined still more new features as premium options. A larger character set includes accented letters for better support of French, Spanish and Portuguese.
The Other Side of Line 21
To date, the digital data for closed captioning have been carried on line 21, field 1 of the vertical blanking interval (VBI), with field 2 left unassigned. Having satisfied the requirement for a decoder able to retrieve data from line 21, receiver manufacturers immediately began to explore other uses for this new information avenue. The EIA, seeking expanded data bandwidth, filed a petition to allow use of line 21, field 2. The FCC agreed, setting aside field 2 for additional channels of captioning as well as Extended Data Services (XDS).
Line 21, field 1 carries four data channels known as CC1 and CC2 (caption channels) and T1 and T2 (text channels). CC1 is the channel for synchronous captionsã the type of captioning available since 1980. CC2 can carry special non-synchronous captions (scrolling text, for example), but not a full-fledged stream of timed and placed caption data. Now, with field 2 as a parallel thoroughfare, four more channels are available- CC3 and CC4 for captions and T3 and T4 for text. A fifth channel, Extended Data Services, is carried in the excess capacity of field 2.
Multilingual Captioning
The most immediate use of line 21, field 2 is for the creation of a second stream of captions. This could allow the viewer to choose between regular captions and edited or "easy reader" captions, or to choose between English captions or captions in Spanish. Many new TV receivers are already equipped with field 2‚capable decoders, and it is expected that most manufacturers will follow suit in the near future.
Extended Data Services
Extended Data Services open a wide array of new uses for the additional VBI real estate. Data packets can contain information which interacts with consumer hardware or other special devices on TVs and VCRs. For example, an XDS packet may set a VCR's clock and calendar, create an index of contents on a videocassette, or tell a VCR when it's time to tape a program. Many innovative uses of XDS are currently being examined and should be in use by 1995.
The basic functionality of a closed-caption decoder is specified in the FCC's Rules (Section 15.119). Amplifications and interpretations, along with recommended practices, are contained in an EIA document known as EIA-608. The EIA document also specifies XDS and defines five separate classes of XDS packets, leaving plenty of room for potential new uses. The defined packets include Current Class (information about the current program such as the title, length, rating, elapsed time, audio services, caption services and aspect ratio), Future Class (the same information for an upcoming program), Channel Information Class (information such as the network name, station call letters, native channel number and tape delay), Miscellaneous Class (containing the time of day and the local time zone) and Public Service Class (severe weather warnings). In addition, Reserved and Undefined Classes are set aside for future expansion and proprietary applications.
A copy of EIA-608 is available from the Electronic Industries Association for $106.
Electronic Industries Association
Engineering Department
2001 Pennsylvania Avenue, N.W.
Washington, DC 20006
202 457-4900
If you currently have or use an encoder, you should contact the vendor of your encoding hardware to inquire about a dual-field encoder upgrade (see TechFacts Vol. 2 - The Lowdown on Upgrades)
When you are ready to discuss these and other exciting new applications, contact The Caption Center! We are prepared to offer you a variety of services using new line-21 capabilities.

To contact us for more information about captioning:
The Caption Center at WGBH
125 Western Avenue
Boston, MA 02134
(617) 300-3600 V/TTY
(617) 300-1020 fax
Los Angeles
300 E. Magnolia Blvd.
2nd Floor
Burbank, CA 91502
818 562-3344 voice
818 562-1919 TTY
818 562-3388 fax
New York
545 Fifth Ave.
Suite 609
New York, NY 10017
212 490-3677 voice
212 490-3688 fax

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