The information on this page pertains to television in the United States only!
On June 12th, 2009, analog television transmission ended in the USA on all major stations as they converted to digital. This update addresses what has become of Video Description.
Formerly Video Description (audio description for television) was delivered to the consumer via the SAP channel. SAP stands for Secondary Audio Program, and it is a unique feature of analog television signal transmission. So, when analog signals ceased, so did the ability to receive Video Description via the SAP audio channel. Well, in most cases anyway...
First, let's cover the exceptions to the preceding statement.
Here's a little more information on point 3 above. A typical cable company sends some of its signals down the line (i.e., the cable port in your wall) in analog, and some in digital -- yes, intermixed in the same signal. Using a local example, the first 72 channels are analog, and the rest are digital. This means a TV without a digital decoder can only receive the first 72 channels. To receive the rest, you need a converter box from the cable company OR what's called a QAM tuner, found in increasing frequency in newer TVs. QAM stands for Quadrature Amplitude Modulation, the format by which digital cable channels are encoded and transmitted via cable. If you have a QAM tuner in your TV, you can receive digital signals without a cable box (provided they are not "scrambled," like premium channels would be).
To receive digital TV signals over the air (as opposed to via cable or satellite), your TV needs a built-in ATSC Tuner, or a converter box (see below).
Now here's the problem: while there is a technical standard (see below) which allows 8 audio channels to be transmitted along with a digital video signal, and one of these channels is specifically for description, the networks haven't agreed to use this channel, and (to the best of our knowledge) no one is selling TVs to consumers today with the capability of receiving these extra audio channels beyond the basic stereo signal associated with TV programs! The engineers at the TV stations know how to put audio on the channels, but why bother, since no one can receive them? Until the FCC mandates the use of a specific channel for video description and mandates that all new TVs manufactured after a certain date be able to receive this (and presumably other) channels, you are unlikely to be able to receive Video Description on a digital TV channel (except as noted above).
(Added December 12, 2009): It is possible that newer cable or satellite set-top converter boxes may have an audio setup option labeled English-2 or Spanish, and these may access video description, when available. If you find that YOU have this capability, please notify the webmaster! We are still at a point when video description has not been mandated and no formal requirement for decoding secondary audio channels on new TVs or converters has been specified. The ACB (American Council of the Blind) has a talented representative (Eric Bridges) on the FCC Working Group which is addressing these issues.
(Added April 23, 2010): WGBH Media Access reports the following experience with one cable TV company (Comcast):
In some areas of the country, Comcast customers are having trouble receiving DVS on programs. Here in Boston, to enable DVS on Comcast's set-top cable box, you need to go into the on-screen menu (using the remote control of the cable box, not using the remote control that came with your TV), select Set-up and then Audio set-up. The twist... you need to enable Spanish. No it is not intuitive, yes, you will need sighted assistance, and no, Comcast customer service usually does not know how to enable the service. This is not the case in all areas (either lack of awareness of the service by Comcast operators or the Spanish to get DVS trick) as technical setup at different Comcast facilities can be handling the TV signal in different ways. The FCC, which set up industry working groups to identify and solve problems with description and captioning in digital television distribution, continues to look at all the issues. We'll continue to keep you informed.
In June 2008, the FCC released a Consumer Advisory on Video Descriptions and the Digital Television Transition. You may click the link to read the advisory.
Digital TV converter boxes are only used if you have an analog TV picking up its signal over the air (i.e., from an antenna); they are not used if you have cable or satellite TV or a digital TV. The government has not specified that these boxes must support audio conversion to SAP. Very few boxes mention SAP in their description. However, the FCC has published a list of converter boxes including those that support SAP, which can be found at FCC Consumer Advisory: Digital-to-Analog Converter Box - Selected Features. We don't know which ones, if any, contain talking menus. Keep in mind that we also don't know if broadcasters will continue to make SAP signals available for the shows that have it today; but purchasing a box which supports SAP is your best protection, if you need a converter at all.
The Advanced Television Systems Committee (ATSC) is an international non-profit organization which develops voluntary standards for digital television (DTV). Their publication, ATSC Digital Television Standard Part 5 — AC-3 Audio System Characteristics, defines the audio channel standards for DTV. The Standard, known as AC-3, specifies eight audio channels, one of which is known as VI (Visually Impaired), technically defined as service type 2 (in the range 0-7, with 0 representing the main audio signal). It further defines a "dynamic range control signal" this channel can use to "turn down" the main channel audio temporarily so description can be heard better. The channel may contain solely description, or the main program material can also be included. It is anticipated that the channel will be used for a merged soundtrack (that is, main program plus description, just like it is today on SAP).
While the FCC has endorsed this standard, the fact remains that many broadcast engineers are unaware of it, and there is no "practical" agreement on its use by broadcasters or implementation in TVs yet. (Thanks to Larry Goldberg of WGBH for supplying information regarding the AC-3 Standard.)
The Media Access Group at WGBH has published an excellent DTV Access page addressing many issues.
Audio description (which on TV or film is often called video description) is offered on a separate (analog) channel on your television known as the SAP or "Secondary Audio Program" channel. This channel is usually disabled and is only used when secondary audio is required.
Secondary audio can offer the program audio in different languages as well as offering access to audio description. If you suddenly find yourself listening to a program in Spanish as you change channels, it is quite possible you accidentally left your SAP enabled.
SAP is available on most stereo televisions and VCRs sold since 1990. The manner in which you will enable your SAP programming is dependent upon your television model. Some televisions offer one-button access to SAP while others require access to an on-screen menu in order to enable the SAP. If you have a television that requires several complicated steps to enable SAP, you may consider checking into an SAP-capable TV or VCR which offers a single button on the remote to enable SAP. (Sony, Panasonic, and Toshiba historically have offered the most TVs with one-button SAP access.)
SAP may be fed through your television by either the television itself or a VCR connected to the television. You may find it convenient to leave your VCR set to receive SAP and simply switch from TV to VCR input when you want to listen to a video described show.
If you are sure that you have properly enabled the SAP channel on your television or VCR and are not receiving the SAP signal for audio described programming, there is probably a problem at either the local television station or the cable company. Special equipment is required at the local level to transmit the SAP signal to your television. The Networks automatically transmit the signal, but it is up to your television station and/or cable/satellite company to pass the signal through to their customers. Technically, the law (overturned in court) only required stations in the top 25 television markets to do this, unless they already had the equipment in place (in which case they must pass along the signal).
If you are not receiving the signal, you may wish to contact your local television station and ask them if they are passing the signal through. If they are, indeed, passing the signal, the next step is to contact your cable or satellite company, if applicable. Remember, SAP only works for analog signals, not digital signals, such as HDTV.
Due to the newness and legal uncertainty of the availability of "video description" (that's what the FCC calls it), many technicians will be unaware of the SAP programming for audio description. Those who are not intimately involved with audio description are generally not overly familiar with the concept. You may need to do a bit of education and explanation.
You may wish to explain the legislation that has passed within your country and ask that the company insure that the signal is being passed through so that you might access the programming. (Note, however, that in November 2002, the FCC ruling requiring "video description" was overturned in the USA, and resolution is still pending all these years later. However, most major networks appear to be offering limited described programming, with PBS leading the way by far, and CBS in second place.)