Video Description Is On the Way

The FCC has recently issued another Report and Order that will affect your life as a television engineer. In FCC 00-258, adopted July 21, 2000, video description is made a requirement for broadcasters and many cablecasters.

Video description would seem to the uninitiated to imply the description of something by the use of video, but in the words of the Report and Order’s introduction, video description is " … the [aural] description of key visual elements in programming, inserted into natural pauses in the audio of the programming." In this way, blind and low-vision persons may more fully share the information imparted by body language, unspoken acting, clothing and other visual aspects of television programming.

PBS and WGBH, Boston, have led this effort for the past decade, with WGBH providing descriptions to accompany programming, and PBS stations providing "closed" description, carried on the station’s SAP channel.

Beginning in the April-June 2002 quarter, video description rules will be in effect as follows: Affiliates of the top four commercial TV networks in the top 25 markets must provide 50 hours per calendar quarter of primetime and/or children’s programming with video description. Multichannel video program distributors (MVPDs) with 50,000 or more subscribers must meet the same requirement on the top five national nonbroadcast networks that they carry.

Additionally, all broadcast stations and MVPDs of any size are required to "pass through" any video description received, providing the station or MVPD has the technical capability to do so. There are also provisions relating to emergency notification information, which will become effective upon approval of the Office of Management and Budget.

DTV was specifically exempted from these rules, with the proviso that the FCC expects to ultimately require video description for DTV programs.


For NTSC television, video description will be broadcast over the SAP channel. According to the Report and Order, NAB survey data suggests that between one-third and one-half of the broadcast stations in the top 25 markets already broadcast on SAP. This is a relatively high-quality signal, as SAP frequency response extends to 10 kHz, and the same noise reduction as that used on the BTSC stereo subchannel is used.

There is one technical hurdle to be cleared, however. Most BTSC receivers will only output main channel audio (stereo or mono) or SAP, but not both simultaneously. Most sets that have SAP capability also have stereo capability, but most have a single BTSC noise reduction expander that can only be used to decode either the stereo subchannel or SAP – but not both at any given time.

To serve this type of receiver, the main program audio will have to be mixed with the descriptive audio, and the balance between the two will necessarily have been set upstream, with no control over it possible at the receiver end.

DTV facilitates two ways to provide video description. The first transmits the descriptive material as a single audio channel, separate from the complete main channel, which may itself contain up to 5.1 channels. The DTV receiver may simultaneously reproduce the complete main audio program and the description material, and the viewer (or in this case the listener) could control the volume balance between complete main audio and descriptive audio.

Alternatively, the video description material may be provided as a complete program mix containing dialog, music, effects and description, coded as any number of channels up to 5.1. In this case main program audio and descriptive audio form a complete main program in their own right, and a special AC-3 descriptor is sent to flag this mode of operation.

Television engineers in the top 25 markets are going to be busy in the summer of 2002, because they are going to be required to implement DTV closed captioning and NTSC video description virtually simultaneously.

Randy Hoffner