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Understanding SC 1.2.4: Captions (Live) (Level AA)

In Brief

Goal
Live videos have captions.
What to do
Provide synchronized text for audio content in real-time videos.
Why it's important
People who are deaf or hard of hearing can understand audio in real-time video content.

Success Criterion (SC)

Captions are provided for all live audio content in synchronized media.

Intent

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.

This success criterion was intended to apply to broadcast of synchronized media and is not intended to require that two-way multimedia calls between two or more individuals through web apps must be captioned regardless of the needs of users. Responsibility for providing captions would fall to the content providers (the callers) or the “host” caller, and not the application.

Benefits

  • People who are deaf or have a hearing loss can access the auditory information in the synchronized media content through captions.

Examples

A Web cast
A news organization provides a live, captioned Web cast.
A music Web cast
An orchestra provides Communication Access Realtime Translation (CART) captioning of each real-time Web performance. The CART service captures lyrics and dialog as well as identifies non-vocal music by title, movement, composer, and any information that will help the user comprehend the nature of the audio.

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques

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. However, it is not necessary to use these particular techniques. For information on using other techniques, see Understanding Techniques for WCAG Success Criteria, particularly the "Other Techniques" section.

Sufficient Techniques

Note

Captions may be generated using real-time text translation service.

Key Terms

ASCII art

picture created by a spatial arrangement of characters or glyphs (typically from the 95 printable characters defined by ASCII)

assistive technology

hardware and/or software that acts as a user agent, or along with a mainstream user agent, to provide functionality to meet the requirements of users with disabilities that go beyond those offered by mainstream user agents

Note

Functionality provided by assistive technology includes 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

Assistive technologies often communicate data and messages with mainstream user agents by using and monitoring APIs.

Note

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 functionality to assistive technologies like retrieving Web content from program objects or parsing markup into identifiable bundles.

audio

the technology of sound reproduction

Note

Audio can be created synthetically (including speech synthesis), recorded from real world sounds, or both.

audio description

narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone

Note

Audio description of video provides information about actions, characters, scene changes, on-screen text, and other visual content.

Note

In standard audio description, narration is added during existing pauses in dialogue. (See also extended audio description.)

Note

Where all of the video information is already provided in existing audio, no additional audio description is necessary.

Note

Also called "video description" and "descriptive narration."

captions

synchronized visual and/or text alternative for both speech and non-speech audio information needed to understand the media content

Note

Captions are similar to dialogue-only subtitles except captions convey not only the content of spoken dialogue, but also equivalents for non-dialogue audio information needed to understand the program content, including sound effects, music, laughter, speaker identification and location.

Note

Closed Captions are equivalents that can be turned on and off with some players.

Note

Open Captions are any captions that cannot be turned off. For example, if the captions are visual equivalent images of text embedded in video.

Note

Captions should not obscure or obstruct relevant information in the video.

Note

In some countries, captions are called subtitles.

Note

Audio descriptions can be, but do not need to be, captioned since they are descriptions of information that is already presented visually.

extended audio description

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 and the pauses between dialogue/narration are too short.

human language

language that is spoken, written or signed (through visual or tactile means) to communicate with humans

Note

See also sign language.

image of text

text that has been rendered in a non-text form (e.g., an image) in order to achieve a particular visual effect

Note

This does not include text that is part of a picture that contains significant other visual content.

live

information captured from a real-world event and transmitted to the receiver with no more than a broadcast delay

Note

A broadcast delay is a short (usually automated) delay, for example used in order to give the broadcaster time to cue or censor the audio (or video) feed, but not sufficient to allow significant editing.

Note

If information is completely computer generated, it is not live.

media alternative for text

media that presents no more information than is already presented in text (directly or via text alternatives)

Note

A media alternative for text is provided for those who benefit from alternate representations of text. Media alternatives for text may be audio-only, video-only (including sign-language video), or audio-video.

non-text content

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), emoticons, leetspeak (which uses character substitution), and images representing text

programmatically determined

determined by software from author-supplied data provided in a way that different user agents, including assistive technologies, can extract and present this information to users in different modalities

sign language

a language using combinations of movements of the hands and arms, facial expressions, or body positions to convey meaning

synchronized media

audio or video synchronized with another format for presenting information and/or with time-based interactive components, unless the media is a media alternative for text that is clearly labeled as such

text

sequence of characters that can be programmatically determined, where the sequence is expressing something in human language

text alternative

Text that is programmatically associated with non-text content or referred to from text that is programmatically associated with non-text content. Programmatically associated text is text whose location can be programmatically determined from the non-text content.

Note

Refer to Understanding Text Alternatives for more information.

user agent

any software that retrieves and presents Web content for users

video

the technology of moving or sequenced pictures or images

Note

Video can be made up of animated or photographic images, or both.

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