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

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

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

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).

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

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.

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;
• speech 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 (including alternate keyboards that use head pointers, single switches, sip/puff and other special input devices.);
• alternative pointing devices, which are used by people with certain physical disabilities to simulate mouse pointing and button activations.

the technology of sound reproduction

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

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

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

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

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

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

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

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.

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

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

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

In some countries, captions are called subtitles.

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

audio description that is added to an audiovisual presentation by pausing the video so that there is time to add additional description

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.

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

See also sign language.

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

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

A person's name on a nametag in a photograph.

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

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.

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

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

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.

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

This includes ASCII Art (which is a pattern of characters), emoticons, leetspeak (which uses character substitution), and images representing text

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

Determined in a markup language from elements and attributes that are accessed directly by commonly available assistive technology.

Determined from technology-specific data structures in a non-markup language and exposed to assistive technology via an accessibility API that is supported by commonly available assistive technology.

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

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

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

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.

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.

Refer to Understanding Text Alternatives for more information.

any software that retrieves and presents Web content for users

Web browsers, media players, plug-ins, and other programs — including assistive technologies — that help in retrieving, rendering, and interacting with Web content.

the technology of moving or sequenced pictures or images

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