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Copyright © 2007 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.
This document, "Understanding WCAG 2.0," is an essential guide to understanding and using Web Content Accessibility Guidelines 2.0 [WCAG20]. It is part of a series of documents that support WCAG 2.0. Please note that the contents of this document are informative (they provide guidance), and not normative (they do not set requirements for conforming to WCAG 2.0).
WCAG 2.0 establishes a set of success criteria to define conformance to the WCAG 2.0 Guidelines. A success criterion is a testable statement that will be either true or false when applied to specific Web content. "Understanding WCAG 2.0" provides detailed information about each success criterion, including its intent, the key terms that are used in the success criterion, and how the success criteria in WCAG 2.0 help people with different types of disabilities. This document also provides examples of Web content that meet the success criterion using various Web technologies (for instance, HTML, CSS, XML), and common examples of Web content that does not meet the success criterion.
This document indicates specific techniques to meet each success criterion. Details for how to implement each technique are available in Techniques and Failures for WCAG 2.0, but "Understanding WCAG 2.0" provides the information about the relationship of each technique to the success criteria. Techniques are categorized by the level of support they provide for the success criteria. "Sufficient techniques" are sufficient to meet a particular success criterion (either by themselves or in combination with other techniques), while other techniques are advisory and therefore optional. None of the techniques are required to meet WCAG 2.0, although some may be the only known method if a particular technology is used. "Advisory techniques" are not sufficient to meet the success criteria on their own (because they are not testable or provide incomplete support) but it is encouraged that authors follow them when possible to provide enhanced accessibility. Another support category is "Failure techniques", which describe authoring practices known to cause Web content not to conform to WCAG 2.0. Although failure techniques provide advisory information about certain authoring practices, authors must avoid those practices in order to meet the WCAG 2.0 success criteria.
This document is part of a series of documents published by the W3C Web Accessibility Initiative (WAI) to support WCAG 2.0.
This document is the internal working draft used by the WCAG WG and is updated continuously and without notice. This document has no formal standing within W3C. Please consult the group's home page and the W3C technical reports index for information about the latest publications by this group.
This draft includes revisions that have been made since the 17 May 2007 Working Draft was published. Please refer to the latest public version of WCAG 2.0 for information about the status of WCAG 2.0 as well as information about submitting comments to the working group.
History of Changes to WCAG 2.0 Working Drafts
Understanding WCAG 2.0 is an essential guide to understanding and using "Web Content Accessibility Guidelines 2.0" [WCAG20] Although the definition and requirements for WCAG 2.0 can all be found in the WCAG 2.0 document itself, the concepts and provisions may be new to some people. Understanding WCAG 2.0 provides an extended commentary on each guideline and each success criterion to help readers better understand the intent and how the guidelines and success criteria work together. It also provides examples of techniques or combinations of techniques that the Working Group has identified as being sufficient to meet each success criterion. Links are then provided to write-ups for each of the techniques.
Editorial Note: Where the committee has not yet been able to write up the description of a techniques, the techniques are listed with "(future link)" following their title.
This is not an introductory document. It is a detailed technical description of the guidelines and their success criteria. For an introduction to WCAG 2.0 and the complete set of documents associated with the guidelines, see Overview of Web Content Accessibility Guidelines (WCAG) 2.0 Documents.
Understanding WCAG 2.0 is organized by guideline. There is an Understanding Guideline X.X section for each guideline. The intent and any advisory techniques that are related to the guideline but not specifically related to any of its success criteria are listed there as well.
The Understanding Guidelines X.X section is then followed by a How to Meet Success Criterion X.X.X section for each success criterion of that guideline. These How to Meet sections each contain:
The success criterion as it appears in WCAG 2.0
Key terms for this success criterion (taken from the WCAG 2.0 Glossary)
Intent of the success criterion
Techniques or combinations of techniques that are sufficient to meet the guidelines
Common failures of this success criterion
Additional advisory techniques that go beyond what is required to meet the success criterion but can be used to make some or all types of content more accessible. Use of advisory techniques does not impact the level of conformance claimed.
Benefits (how the success criterion helps people with disabilities)
Examples
Related Resources
Links are provided from each Guideline in WCAG 2.0 directly to each Understanding Guideline X.X in this document. Similarly, there is a link from each success criterion in WCAG 2.0 to the How to Meet Success Criterion X.X.X section in this document.
For information about individual techniques, follow the links throughout this document to the techniques of interest in the Techniques for WCAG 2.0 document.
The guidelines and success criteria are organized around the following four principles. These four principles lay the foundation necessary for anyone to access and use Web content. Anyone who wants to use the Web must have content that is:
Perceivable - Information and user interface components must be perceivable by users
This means that users must be able to perceive the information being presented (it can't be invisible to all of their senses)
Operable - User interface components must be operable by users
This means that users must be able to operate the interface (the interface cannot require interaction that the user can not perform)
Understandable - Information and operation of user interface must be understandable by users
This means that users must be able to understand the information as well as the operation of the user interface (the content or operation cannot be beyond their understanding)
Robust - Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies
This means that users must be able to access the content as technologies advance (as technologies and user agents evolve, the content should remain accessible)
If any of these are not true, users with disabilities will not be able to use the Web.
Under each of the principles are guidelines and success criteria that help to address these principles for people with disabilities. There are many general usability guidelines that make content more usable by all people, including those with disabilities. However, in WCAG 2.0, we only include those guidelines that address problems particular to people with disabilities. This includes issues that block access or interfere with access to the Web more severely for people with disabilities.
The purpose of this guideline is to ensure that all non-text content is also available in text. "Text" refers to electronic text, not an image of text. Electronic text has the unique advantage that it can be rendered visually, auditorially, tactilely, or by any combination. As a result, information rendered in electronic text can be presented in whatever form best meets the needs of the user. It can also be easily enlarged, spoken in a voice that is easy to understand, or rendered in whatever tactile form best meets the needs of a user.
Specific techniques for meeting each success criterion for this guideline are listed in the understanding sections for each success criterion (listed below). If there are techniques, however, for addressing this guideline that do not fall under any of the success criteria, they are listed here. These techniques are not required or sufficient for meeting any success criteria, but can make certain types of Web content more accessible to more people.
Providing sign language videos for audio-only files (future link)
1.1.1 All non-text content has a text alternative that presents equivalent information, except for the situations listed below. (Level A)
Controls, Input: If it is a control or accepts user input, then it has a name that describes its purpose. (See also Guideline 4.1.)
Media, Test, Sensory: If it is any of the following, then text alternatives at least identify the non-text content with a descriptive text label: multimedia, live audio-only or live video-only content, a test or exercise that must be presented in non-text format, or content primarily intended to create a specific sensory experience. (For multimedia, see also Guideline 1.2.)
CAPTCHA: If it is to confirm that content is being accessed by a person rather than a computer, then text alternatives that identify and describe the purpose of the non-text content are provided, and alternative forms of CAPTCHA using output modes for different types of sensory perception are provided to accommodate different disabilities.
Decoration, Formatting, Invisible: If it is pure decoration, or used only for visual formatting, or if it is not presented to users, then it is implemented in a way that it can be ignored by assistive technology.
The intent of this success criterion is to make information conveyed by non-text content accessible through the use of a text alternative. Text alternatives are a primary way for making information accessible because they can be rendered through any sensory modality (for example, visual, auditory or tactile) to match the needs of the user. Providing text alternatives allows the information to be rendered in a variety of ways by a variety of user agents. For example, a person who cannot see a picture can have the text alternative read aloud using synthesized speech. A person who cannot hear an audio file can have the text alternative displayed so that he or she can read it. In the future, text alternatives will also allow information to be more easily translated into sign language or into a simpler form of the same language.
Non-text content can take a number of forms, and this success criterion specifies how each is to be handled.
For non-text content that is not covered by one of the other situations listed below, such as charts, diagrams, audio recordings, pictures, and animations, text alternatives can make the same information available in a form that can be rendered through any modality (for example, visual, auditory or tactile). Short and long text alternatives can be used as needed to convey the information in the non-text content. Note that prerecorded audio-only and prerecorded video-only files are covered here. Live-audio-only and Live-video-only files are covered below (see 3rd paragraph following this one).
For non-text content that is a control or accepts user input , such as images used as submit buttons or complex animations, a name is provided to describe the purpose of the non-text content so that the person at least knows what the non-text content is and why it is there.
Non-text content that is multimedia is made accessible through guideline 1.2. However it is important that users know what it is when they encounter it on a page so they can decide what action if any they want to take with it. A text alternative that describes the multimedia and/or gives its title is therefore provided.
Live Audio-only and live video-only files - It is much more difficult to provide text alternatives that convey the same information as live audio-only and live video-only content. For these types of non-text content, text alternatives provide a descriptive label.
Sometimes a test or exercise must use a particular sense. Audio or visual information is provided that cannot be changed to text because the test or exercise must be conducted using that sense. For example, a hearing test would be invalid if a text alternative were provided. A visual skill development exercise would similarly make no sense in text form. And a spelling test with text alternatives would not be very effective. For these cases, text alternatives should be provided to describe the purpose of the non-text content; of course, the text alternatives would not provide the same information needed to pass the test.
Sometimes content is primarily intended to create a specific sensory experience that words cannot fully capture. Examples include a symphony performance, works of visual art etc. For such content, text alternatives at least identify the non-text content with a descriptive label and where possible, some descriptive text. If the reason for including the content in the page is known and can be described it is helpful to include that information.
Sometimes there are non-text exercises that are used to prove you are human. To avoid spam robots and other software from gaining access to a site a device called a CAPTCHA is used. These usually involve visual or auditory tasks that are beyond the current capabilities of web robots. Providing a text alternative to them would however make them operable by Robots, thus defeating their purpose. In this case a text alternative would describe the purpose of the CAPTCHA, and alternate forms using different modalities would be provided to address the needs of people with different disabilities.
Sometimes there is non-text content that really is not meant to be seen or understood by the user. Transparent images used to move text over on a page; a one pixel transparent "web-bug" that tells the author when the page is viewed; and a swirl in the corner that conveys no information but just fills up a blank space to create an aesthetic effect are all examples of this. Putting alternative text on such items just distracts people using screen readers from the content on the page. Not marking the content in any way, though, leaves users guessing what the non-text content is and what information they may have missed (even though they have not missed anything in reality). This type of non-text content, therefore, is marked or implemented in a way that assistive technologies (AT) will ignore it and not present anything to the user.
This success criterion helps people who have difficulty perceiving visual content. Assistive technology can read text alternatives aloud, present them visually, or convert them to braille.
Text alternatives may help some people who have difficulty understanding the meaning of photographs, drawings, and other images (e.g. line drawings, graphic designs, paintings, three-dimensional representations), graphs, charts, animations, etc.
People who are deaf, are hard of hearing, or who are having trouble understanding audio information for any reason can read the text presentation. Research is ongoing regarding automatic translation of text into sign language.
People who are deaf-blind can read the text in braille.
Additionally, text alternatives support the ability to search for non-text content and to repurpose content in a variety of ways.
A data chart
A bar chart compares how many widgets were sold in June, July, and August. The short label says, "Figure one - Sales in June, July and August." The longer description identifies the type of chart, provides a high-level summary of the data, trends and implications comparable to those available from the chart. Where possible and practical, the actual data is provided in a table.
An audio recording of a speech (no video)
The link to an audio clip says, "Chairman's speech to the assembly." A link to a text transcript is provided immediately after the link to the audio clip.
An animation that illustrates how a car engine works
An animation shows how a car engine works. There is no audio and the animation is part of a tutorial that describes how an engine works. Since the text of the tutorial already provides a full explanation, the text alternative has a brief description of the image and refers to the tutorial text for more information.
A traffic Web camera
A Web site allows users to select from a variety of Web cameras positioned throughout a major city. After a camera is selected, the image updates every two minutes. A short text alternative identifies the Web camera as "traffic Web camera." The site also provides a table of travel times for each of the routes covered by the Web cameras. The table is also updated every two minutes.
A photograph of an historic event in a news story
A photograph of two world leaders shaking hands accompanies a news story about an international summit meeting. The text alternative says, "President X of Country X shakes hands with Prime Minister Y of country Y."
A photograph of a historic event in content discussing diplomatic relationships
The same image is used in a different context intended to explain nuances in diplomatic encounters. The image of the president shaking hands with the prime minister appears on a Web site discussing intricate diplomatic relationships. The first text alternative reads, "President X of country X shakes hands with Prime Minister Y of country Y on January 2, 2009." An additional text alternative describes the room where the leaders are standing as well as the expressions on the leaders' faces, and identifies the other people in the room. The additional description might be included on the same page as the photograph or in a separate file associated with the image through a link or other standard programmatic mechanism.
An audio recording
The Web page described in the previous example includes a link to an audio recording of the leaders' press conference. The page also links to a text transcript of the press conference. The transcript includes a verbatim record of everything the speakers say. It identifies who is speaking as well as noting other significant sounds that are part of the recording, such as applause, laughter, questions from the audience, and so on.
An e-learning application
An e-learning application uses sound effects to indicate whether or not the answers are correct. The chime sound indicates that the answer is correct and the beep sound indicates that the answer is incorrect. A text description is also included so that people who can't hear or understand the sound understand whether the answer is correct or incorrect.
A linked thumbnail image
A thumbnail image of the front page of a newspaper links to the home page of the "Smallville Times". The text alternative says "Smallville Times".
Different alternatives for an image of the world: An image of the world that is used on a travel site as a link to the International Travel section has the text alternative "International Travel". The same image is used as a link on a university Web site with the text alternative "International Campuses".
Resources are for information purposes only, no endorsement implied.
Excerpts from the NBA Tape Recording Manual, Third Edition. Information on describing complex images to people who are blind.
Inaccessibility of CAPTCHA. Examines a number of potential solutions that allow systems to test for human users while preserving access by users with disabilities.
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
Instructions: Select the situation below that matches your content. Each situation includes numbered techniques (or combinations of techniques) that the Working Group deems to be sufficient for that situation.
G94: Providing short text alternative for non-text content that serves the same purpose and presents the same information as the non-text content using a short text alternative technique listed below
G95: Providing short text alternatives that provide a brief description of the non-text content using a short text alternative technique listed below AND one of the following techniques for long description:
G92: Providing long description for non-text content that serves the same purpose and presents the same information using a long text alternative technique listed below
G82: Providing a text alternative that identifies the purpose of the non-text content using a short text alternative technique listed below
Using HTML form controls and links (future link)
H44: Using label elements to associate text labels with form controls (HTML)
H65: Using the title attribute to identify form controls when the label element cannot be used (HTML)
Using (X)HTML according to spec (future link)
Providing a descriptive label using a short text alternative technique listed below
G68: Providing a descriptive label that describes the purpose of live audio-only and live video-only content using a short text alternative technique listed below
G100: Providing the accepted name or a descriptive name of the non-text content using a short text alternative technique listed below
Implementing or marking the non-text content so that it will be ignored by assistive technology using one of the technology-specific techniques listed below
H36: Using alt attributes on images used as submit buttons (HTML)
H24: Providing text alternatives for the area elements of image maps (HTML)
Providing text alternatives for strings where look-alike glyphs are used in place of letters (e.g. leetspeak) (future link)
Providing text alternatives for ASCII art (future link)
The following are common mistakes that are considered failures of Success Criterion 1.1.1 by the WCAG Working Group.
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
Identifying informative non-text content (future link)
Keeping short descriptions short (future link)
Describing images that include text (future link)
Providing a longer description of the non-text content where only a descriptive label is required using a technology-specific technique (for an accessibility-supported content technology) for long description listed above (future link)
Linking to textual information that provides comparable information (e.g. for a traffic Webcam, a municipality could provide a link to the text traffic report.) (future link)
Providing a transcript of a live audio only presentation after the fact (future link)
Writing for browsers that do not support frame
Providing alternative content for iframe
H27: Providing text and non-text alternatives for object (HTML)
Not using long descriptions for iframe
Providing redundant text links for client-side image maps (future link)
Hardware and/or software that acts as a user agent, or along with a mainstream user agent, to provide services to meet the requirements of users with disabilities that go beyond those offered by the mainstream user agents. Such services include alternative presentations (e.g., as synthesized speech or magnified content), alternative input methods (e.g., voice), additional navigation or orientation mechanisms, and content transformations (e.g., to make tables more accessible)
Note 1: The distinction between mainstream user agents and assistive technologies is not absolute. Many mainstream user agents provide some features to assist individuals with disabilities. The basic difference is that mainstream user agents target broad and diverse audiences that usually include people with and without disabilities. Assistive technologies target narrowly defined populations of users with specific disabilities. The assistance provided by an assistive technology is more specific and appropriate to the needs of its target users. The mainstream user agent may provide important services to assistive technologies like retrieving Web content from program objects or parsing markup into identifiable bundles.
Example: Examples of assistive technologies that are important in the context of this document include the following:
screen magnifiers, and other visual reading assistants, which are used by people with visual, perceptual and physical print disabilities to change text font, size, spacing, color, synchronization with speech, etc. in order to improve the visual readability of rendered text and images;
screen readers, which are used by people who are blind to read textual information through synthesized speech or braille;
text-to-speech software, which is used by some people with cognitive, language, and learning disabilities to convert text into synthetic speech;
voice recognition software, which may be used by people who have some physical disabilities;
alternative keyboards, which are used by people with certain physical disabilities to simulate the keyboard;
alternative pointing devices, which are used by people with certain physical disabilities to simulate mouse pointing and button activations.
initialism for "Completely Automated Public Turing test to tell Computers and Humans Apart"
Note 1: CAPTCHA tests often involve asking the user to type in text that is displayed in an obscured image or audio file.
Note 2: A Turing test is any system of tests designed to differentiate a human from a computer. It is named after famed computer scientist Alan Turing. The term was coined by researchers at Carnegie Mellon University. [CAPTCHA]
text or other component with a text alternative that is presented to a user to identify a component within Web content
Note: A label is presented to all users whereas the name may be hidden and only exposed by assistive technology. In many (but not all) cases the name and the label are the same.
A time-based live presentation that contains only audio (no video and no interaction)
A time-based live presentation that contains only video (no audio and no interaction)
audio or video synchronized with another format for presenting information and/or with time-based interactive components
would be invalid if presented in text
Example: Color blindness test, hearing test, vision exercise, spelling test.
text by which software can identify a component within Web content to the user
Note 1: The name may be hidden and only exposed by assistive technology, whereas a label is presented to all users. In many (but not all) cases, the label and the name are the same.
Note 2: This is unrelated to the name attribute in HTML.
any content that is not a sequence of characters that can be programmatically determined or where the sequence is not expressing something in human language
Note: This includes ASCII Art (which is a pattern of characters), leetspeak (which is character substitution), and images representing text.
serving only an aesthetic purpose, providing no information, and having no functionality
Note: Text is only purely decorative if the words can be rearranged or substituted without changing their purpose.
Example: The cover page of a dictionary has random words in very light text in the background.
a sensory experience that is not purely decorative and does not primarily convey important information or perform a function
Example: Examples include a performance of a flute solo, works of visual art etc.
programmatically determined text that is used in place of non-text content, or text that is used in addition to non-text content and referred to from the programmatically determined text
Example: An image of a chart is described in text in the paragraph after the chart. The short text-alternative for the chart indicates that a description follows.
1.1.2 All live audio-only content has a text alternative (Level AAA)
Editorial Note: Not yet drafted. Refer to Issue 1944.
The purpose of this guideline is to provide access to multimedia. Multimedia is defined in the glossary as:
multimedia: audio or video synchronized with another type of media and/or with time-based interactive components
Note that an audio file accompanied by interaction is covered here, as is a video-only file that involves interaction. These are covered because interaction must take place at a particular time. Having a text transcript that said, "for more information, click now," would not be very helpful since the reader would have no idea when the audio said, "now." As a result, synchronized captions would be needed.
Sometimes, there is so much dialogue that audio description cannot fit into existing pauses in the dialogue. The option at Level A to provide a full text alternative for multimedia including any interaction instead of audio description for multimedia would allow access to all of the information in the multimedia. This option also allows access to the visual information in non-visual form when audio description is not provided for some other reason.
For multimedia that includes interaction, interactive elements (for example links) could be embedded in the full text alternative for multimedia.
This guideline also includes (at Level AAA) sign language interpretation for multimedia as well as an approach called extended audio description. In extended audio description, the video is frozen periodically to allow more audio description to take place than is possible in the existing pauses in the dialogue. This is a case where higher-level success criteria build upon the requirements of lower-level SC with the intention of having cumulative, progressively stronger, requirements.
Specific techniques for meeting each success criterion for this guideline are listed in the understanding sections for each success criterion (listed below). If there are techniques, however, for addressing this guideline that do not fall under any of the success criteria, they are listed here. These techniques are not required or sufficient for meeting any success criteria, but can make certain types of Web content more accessible to more people.
Providing audio description for live multimedia (future link)
1.2.1 Captions are provided for prerecorded multimedia, except for multimedia alternatives to text that are clearly labeled as such. (Level A)
The intent of this success criterion is to enable people who are deaf or hard of hearing to watch multimedia presentations. Captions provide the part of the content available via the audio track. Captions not only include dialogue, but identify who is speaking and include non-speech information conveyed through sound, including meaningful sound effects.
It is acknowledged that at the present time there may be difficulty in creating captions for time-sensitive material and this may result in the author being faced with the choice of delaying the information until captions are available, or publishing time-sensitive content that is inaccessible to the deaf, at least for the interval until captions are available. Over time, the tools for captioning as well as building the captioning into the delivery process can shorten or eliminate such delays.
Captions are not needed when the multimedia is, itself, an alternate presentation of information that is also presented via text on the Web page. For example, if information on a page is accompanied by a multimedia presentation that presents no more information than is already presented in text, but is easier for people with cognitive, language, or learning disabilities to understand, then it would not need to be captioned since the information is already presented on the page in text or in text alternatives (e.g. for images).
People who are deaf or have a hearing loss can access the auditory information in the multimedia content through captions.
A captioned tutorial
A video clip shows how to tie a knot. The captions read,
"(music)
Using rope to tie knots was an important skill
for the likes of sailors, soldiers and woodsmen.."
From Sample Transcript Formatting by Whit Anderson.
A complex legal document contains multimedia clips for different paragraphs that show a person speaking the contents of the paragraph. Each clip is associated with its corresponding paragraph. No captions are provided for the multimedia.
An instruction manual containing a description of a part and its necessary orientation is accompanied by a multimedia clip showing the part in its correct orientation. No captions are provided for the multimedia clip.
Resources are for information purposes only, no endorsement implied.
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
G87: Providing closed captions using any readily available media format that has a video player that supports closed captioning
G87: Providing closed captions using any of the technology-specific techniques below
The following are common mistakes that are considered failures of Success Criterion 1.2.1 by the WCAG Working Group.
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
Providing a note saying "No sound is used in this clip" for video-only clips (future link)
Using SMIL 1.0 to provide captions for all languages for which there are audio tracks (future link)
Using SMIL 2.0 to provide captions for all languages for which there are audio tracks (future link)
text presented and synchronized with multimedia to provide not only the speech, but also non-speech information conveyed through sound, including meaningful sound effects and identification of speakers
Note 1: In some countries, the term "subtitle" is used to refer to dialogue only and "captions" is used as the term for dialogue plus sounds and speaker identification. In other countries, subtitle (or its translation) is used to refer to both.
Note 2: Audio descriptions can be, but do not need to be, captioned since they are descriptions of information that is already presented visually.
audio or video synchronized with another format for presenting information and/or with time-based interactive components
multimedia that presents no more information than is already presented in text (directly or via text alternatives)
Note: Multimedia alternatives to text are provided for those who benefit from alternate representations of text.
1.2.2 Audio description of video, or a full text alternative for multimedia including any interaction , is provided for prerecorded multimedia. (Level A)
Note: For 1.2.2, 1.2.4, and 1.2.7, if all of the information in the video track is already provided in the audio track, no audio description is necessary.
The intent of this success criterion is to provide people who are blind or visually impaired access to the visual information in a multimedia presentation. This success criterion describes two approaches, either of which can be used.
One approach is to provide audio description of the video content. The audio description augments the audio portion of the presentation with the information needed when the video portion is not available. During existing pauses in dialogue, audio description provides information about actions, characters, scene changes, and on-screen text that are important and are not described or spoken in the main sound track.
The second approach involves providing all of the information in the multimedia (both visual and auditory) in text form. A full text alternative for multimedia including any interaction provides a running description of all that is going on in the multimedia content. The full text alternative for multimedia including any interaction reads something like a screenplay or book. Unlike audio description, the description of the video portion is not constrained to just the pauses in the existing dialogue. Full descriptions are provided of all visual information, including visual context, actions and expressions of actors, and any other visual material. In addition, non-speech sounds (laughter, off-screen voices, etc.) are described, and transcripts of all dialogue are included. The sequence of description and dialogue transcripts are the same as the sequence in the multimedia itself. As a result, the full text alternative for multimedia can provide a much more complete representation of the multimedia content than audio description alone.
If there is any interaction as part of the multimedia presentation (e.g. "press now to answer the question") then the full text alternative for multimedia would provide hyperlinks or whatever is needed to provide the same functionality.
Note 1: For 1.2.2, 1.2.3, and 1.2.7, if all of the information in the video track is already provided in the audio track, no audio description is necessary.
Note 2: 1.2.2, 1.2.4, and 1.2.7 overlap somewhat with each other. This is to give the author some choice at the minimum conformance level, and to provide additional requirements at higher levels. At Level A in SC 1.2.2, authors do have the choice of providing either an audio description or a full text alternative. If they wish to conform at Level AA, under SC 1.2.4 authors must provide an audio description - a requirement already met if they chose that alternative for 1.2.2, otherwise an additional requirement. At Level AAA under SC 1.2.7 they must provide an extended text description. This is an additional requirement if both 1.2.2 and 1.2.4 were met by providing an audio description only. If 1.2.2 was met, however, by providing a text description, and the 1.2.4 requirement for an audio description was met, then 1.2.7 does not add new requirements.
This success criterion may help some people who have difficulty watching video or other multimedia content, including people who have difficulty perceiving or understanding moving images.
A movie with audio description.
Describer: A title, "Teaching Evolution Case Studies. Bonnie Chen." A teacher shows photographs of birds with long, thin beaks.
Bonnie Chen: "These photos were all taken at the Everglades."
Describer: The teacher hands each student two flat, thin wooden sticks.
Bonnie Chen: "Today you will pretend to be a species of wading bird that has a beak like this."
Describer: The teacher holds two of the sticks to her mouth making the shape of a beak.
Transcript of audio based on the first few minutes of "Teaching Evolution Case Studies, Bonnie Chen" (copyright WGBH and Clear Blue Sky Productions, Inc.)
A full text alternative for multimedia including any interaction for a training video
A company purchases a Training video for use by its employees and puts it on the companies intranet. The video involves explaining use of a new technology and has a person talking and showing things at the same time. Since there is no place to insert audio description of the visual demonstrations during gaps in dialogue, the company provides a full text alternative for multimedia that all employees, including those who cannot see the demonstrations, can use to better understand what is being presented.
Resources are for information purposes only, no endorsement implied.
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
G69: Providing a full multimedia text alternative including any interaction
G78: Providing a sound track that includes audio description as the primary sound track
G78: Providing a sound track that includes audio description AND associating it with the multimedia content using one of the following techniques:
Providing audio description in its own sound track (future link) AND merging the description track with the original soundtrack of the multimedia content at runtime using one of the following techniques
Using SMIL 1.0 to merge a description track with sound track (future link)
Using SMIL 2.0 to merge a description track with sound track (future link)
The following are common mistakes that are considered failures of Success Criterion 1.2.2 by the WCAG Working Group.
(No failures currently documented)
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
Providing audio description in multiple languages in SMIL 1.0 (future link)
Providing audio description in multiple languages in SMIL 2.0 (future link)
narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone
Note 1: Audio description of video provides information about actions, characters, scene changes, on-screen text, and other visual content.
Note 2: In standard audio description, narration is added during existing pauses in dialogue. (See also extended audio description.)
Note 3: Also called "video description" and "descriptive narration."
document including correctly sequenced text descriptions of all visual settings, actions, speakers, and non-speech sounds, and transcript of all dialogue combined with a means of achieving any outcomes that are achieved using interaction (if any) during the multimedia
Note: A screenplay used to create the multimedia content would meet this definition only if it was corrected to accurately represent the final multimedia after editing.
audio or video synchronized with another format for presenting information and/or with time-based interactive components
1.2.3 Captions are provided for live multimedia. (Level AA)
Note: If multimedia is completely computer generated, it is not live and is subject to the requirements for prerecorded multimedia in WCAG 2.0.
The intent of this success criterion is to enable people who are deaf or hard of hearing to watch real-time presentations. Captions provide the part of the content available via the audio track. Captions not only include dialogue, but also identify who is speaking and notate sound effects and other significant audio.
People who are deaf or have a hearing loss can access the auditory information in the multimedia content through captions.
A Web cast
A news organization provides a live, captioned Web cast.
Resources are for information purposes only, no endorsement implied.
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
G9: Creating captions for live multimedia AND G93: Providing open (always visible) captions
G9: Creating captions for live multimedia AND G87: Providing closed captions using any readily available media format that has a video player that supports closed captioning
G9: Creating captions for live multimedia AND G87: Providing closed captions using one of the following techniques:
Note: Captions may be generated using real-time text translation service.
The following are common mistakes that are considered failures of Success Criterion 1.2.3 by the WCAG Working Group.
(No failures currently documented)
text presented and synchronized with multimedia to provide not only the speech, but also non-speech information conveyed through sound, including meaningful sound effects and identification of speakers
Note 1: In some countries, the term "subtitle" is used to refer to dialogue only and "captions" is used as the term for dialogue plus sounds and speaker identification. In other countries, subtitle (or its translation) is used to refer to both.
Note 2: Audio descriptions can be, but do not need to be, captioned since they are descriptions of information that is already presented visually.
audio or video synchronized with another format for presenting information and/or with time-based interactive components
1.2.4 Audio description of video is provided for prerecorded multimedia. (Level AA)
The intent of this success criterion is to provide people who are blind or visually impaired access to the visual information in a multimedia presentation. The audio description augments the audio portion of the presentation with the information needed when the video portion is not available. During existing pauses in dialogue, audio description provides information about actions, characters, scene changes, and on-screen text that are important and are not described or spoken in the main sound track.
Note 1: For 1.2.2, 1.2.3, and 1.2.7, if all of the information in the video track is already provided in the audio track, no audio description is necessary.
Note 2: 1.2.2, 1.2.4, and 1.2.7 overlap somewhat with each other. This is to give the author some choice at the minimum conformance level, and to provide additional requirements at higher levels. At Level A in SC 1.2.2, authors do have the choice of providing either an audio description or a full text alternative. If they wish to conform at Level AA, under SC 1.2.4 authors must provide an audio description - a requirement already met if they chose that alternative for 1.2.2, otherwise an additional requirement. At Level AAA under SC 1.2.7 they must provide an extended text description. This is an additional requirement if both 1.2.2 and 1.2.4 were met by providing an audio description only. If 1.2.2 was met, however, by providing a text description, and the 1.2.4 requirement for an audio description was met, then 1.2.7 does not add new requirements.
People who are blind or have low vision as well as those with cognitive limitations who have difficulty interpreting visually what is happening benefit from audio description of visual information.
A movie with audio description.
Describer: A title, "Teaching Evolution Case Studies. Bonnie Chen." A teacher shows photographs of birds with long, thin beaks.
Bonnie Chen: "These photos were all taken at the Everglades."
Describer: The teacher hands each student two flat, thin wooden sticks.
Bonnie Chen: "Today you will pretend to be a species of wading bird that has a beak like this."
Describer: The teacher holds two of the sticks to her mouth making the shape of a beak.
Transcript of audio based on the first few minutes of "Teaching Evolution Case Studies, Bonnie Chen" (copyright WGBH and Clear Blue Sky Productions, Inc.)
Resources are for information purposes only, no endorsement implied.
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
G78: Providing a sound track that includes audio description as the primary sound track
G78: Providing a sound track that includes audio description AND associating it with the multimedia content using one of the following techniques:
Providing audio description in its own sound track (future link) AND merging the description track with the original soundtrack of the multimedia content at runtime using one of the following techniques
Using SMIL 1.0 to merge a description track with sound track (future link)
Using SMIL 2.0 to merge a description track with sound track (future link)
The following are common mistakes that are considered failures of Success Criterion 1.2.4 by the WCAG Working Group.
(No failures currently documented)
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
Providing audio description in multiple languages in SMIL 1.0 (future link)
Providing audio description in multiple languages in SMIL 2.0 (future link)
narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone
Note 1: Audio description of video provides information about actions, characters, scene changes, on-screen text, and other visual content.
Note 2: In standard audio description, narration is added during existing pauses in dialogue. (See also extended audio description.)
Note 3: Also called "video description" and "descriptive narration."
audio or video synchronized with another format for presenting information and/or with time-based interactive components
1.2.5 Sign language interpretation is provided for multimedia. (Level AAA)
The intent of this success criterion is to enable people who are deaf or hard of hearing and who are fluent in a sign language to understand the content of the audio track of multimedia presentations. Written text, such as that found in captions, is often a second language. Because sign language provides the ability to provide intonation, emotion and other audio information that is reflected in sign language interpretation, but not in captions, sign language interpretation provides richer and more equivalent access to multimedia. People who communicate extensively in sign language are also faster in sign language and multimedia is a time-based presentation.
People whose human language is a sign language sometimes have limited reading ability. These individuals may not be able to read and comprehend the captions and thus require a sign language interpretation to gain access to the multimedia content.
Example 1. A corporation is making an important announcement to all of its employees. The meeting will be held in the main headquarters and streamed to the Web. A sign language interpreter is provided at the meeting location. The live video includes a full view of the sign language interpreter as well as the person presenting.
Example 2. The same announcement described in example 1 is also Webcast to remote employees. Since there is only one display available for this, the sign language interpreter is shown in the corner of the display.
Example 3. A university is providing an on-line version of a particular lecture by creating a multimedia presentation of the professor delivering the lecture. The presentation includes video of the professor speaking and demonstrating a science experiment. A sign language interpretation of the lecture is created and presented on the Web with the multimedia version.
Resources are for information purposes only, no endorsement implied.
National Institute on Deafness and other Communication Disorders: Information on American Sign Language
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
G54: Including a sign language interpreter in the video stream
Providing a new page that has the video with the sign language interpretation of the audio track (future link)
G81: Providing a synchronized video of the sign language interpreter that can be displayed in a different viewport or overlaid on the image by the player using one of the following techniques
The following are common mistakes that are considered failures of Success Criterion 1.2.5 by the WCAG Working Group.
(No failures currently documented)
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
(none currently documented)
audio or video synchronized with another format for presenting information and/or with time-based interactive components
translation of one language, generally a spoken language, into a sign language
Note: True sign languages are independent languages that are unrelated to the spoken language(s) of the same country or region.
1.2.6 Extended audio description of video is provided for prerecorded multimedia. (Level AAA)
The intent of this success criterion is to provide people who are blind or visually impaired access to a multimedia presentation beyond that which can be provided by standard audio description. This is done by periodically freezing the multimedia presentation and playing additional audio description. The multimedia presentation is then resumed.
Because it disrupts viewing for those who do not need the additional description, techniques that allow you to turn the feature on and off are often provided. Alternately, versions with and without the additional description can be provided.
People who are blind, people with low vision who cannot see the screen, as well as those with cognitive limitations who have difficulty interpreting visually what is happening, often use audio description of the visual information. However, if there is too much dialogue the audio description is insufficient. Extended audio description can provide the additional information they needed to understand the video.
Example 1. Video of a lecture. A physics professor is giving a lecture. He makes freehand sketches on the whiteboard, speaking rapidly as he draws. As soon as he has finished discussing one problem, he erases the drawing and makes another sketch while continuing to speak and gesture with his other hand. The video is paused between problems, and extended audio description of the professor’s drawings and gestures is provided; the video is then resumed.
Resources are for information purposes only, no endorsement implied.
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
Providing a second version of the movie with extended audio descriptions during halted video segments (future link)
G8: Creating an extended audio description for the multimedia content using one of the following techniques
The following are common mistakes that are considered failures of Success Criterion 1.2.6 by the WCAG Working Group.
(No failures currently documented)
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
Adding extended audio description in multiple languages in SMIL 1.0 (future link)
Adding extended audio description in multiple languages in SMIL 2.0 (future link)
audio description that is added to an audiovisual presentation by pausing the video so that there is time to add additional description
Note: This technique is only used when the sense of the video would be lost without the additional audio description.
audio or video synchronized with another format for presenting information and/or with time-based interactive components
1.2.7 A full text alternative for multimedia including any interaction is provided for all prerecorded multimedia, except for multimedia alternatives to text that are clearly labeled as such. (Level AAA)
The intent of this success criterion is to make audio visual material available to individuals whose vision is too poor to reliably read captions and whose hearing is too poor to reliably hear dialogue and audio description. This is done by providing a full text alternative for multimedia including any interaction.
This approach involves providing all of the information in the multimedia (both visual and auditory) in text form. A full text alternative for multimedia including any interaction provides a running description of all that is going on in the multimedia content. The full text alternative for multimedia reads something like a book. Unlike audio description, the description of the video portion is not constrained to just the pauses in the existing dialogue. Full descriptions are provided of all visual information, including visual context, actions and expressions of actors, and any other visual material. In addition, non-speech sounds (laughter, off-screen voices, etc.) are described, and transcripts of all dialogue are included. The sequence of descriptions and dialogue transcripts is the same as the sequence in the multimedia itself. As a result, the full text alternative for multimedia can provide a much more complete representation of the multimedia content than audio description alone.
If there is any interaction as part of the multimedia presentation (e.g. "press now to answer the question") then the full text alternative for multimedia would provide hyperlinks or whatever is needed to provide parallel functionality.
Individuals whose vision is too poor to reliably read captions and whose hearing is too poor to reliably hear dialogue can access the full text alternative for multimedia by using a refreshable braille display.
Note 1: For 1.2.2, 1.2.3, and 1.2.7, if all of the information in the video track is already provided in the audio track, no audio description is necessary.
Note 2: 1.2.2, 1.2.4, and 1.2.7 overlap somewhat with each other. This is to give the author some choice at the minimum conformance level, and to provide additional requirements at higher levels. At Level A in SC 1.2.2, authors do have the choice of providing either an audio description or a full text alternative. If they wish to conform at Level AA, under SC 1.2.4 authors must provide an audio description - a requirement already met if they chose that alternative for 1.2.2, otherwise an additional requirement. At Level AAA under SC 1.2.7 they must provide an extended text description. This is an additional requirement if both 1.2.2 and 1.2.4 were met by providing an audio description only. If 1.2.2 was met, however, by providing a text description, and the 1.2.4 requirement for an audio description was met, then 1.2.7 does not add new requirements.
People who cannot see well or at all and who also cannot hear well or at all can get access to information in audio-visual presentations.
Example 1. full text alternative for multimedia for a training video
A community center purchases a Training video for use by its clients and puts it on the center’s intranet. The video involves explaining use of a new technology