Web Content Accessibility Guidelines (WCAG) for Closed Captions

Updated November 14, 2023


The WCAG are a set of standards that are part of the Web Accessibility Initiative (WAI) by the World Wide Web Consortium (W3C). They are developed to ensure that web content is accessible to people with disabilities, including specific guidelines to ensure that web video is accessible to individuals with hearing impairments.

WCAG is widely regarded as a best practice for web accessibility. Some countries have incorporated accessibility standards based on WCAG into national laws and regulations, making them legally binding. In addition, many organizations voluntarily adopt WCAG to ensure that their websites and digital services are inclusive.

WCAG versions

WCAG has undergone several versions since its initial release. Each version represents an advancement in addressing accessibility challenges. The W3C continues to work on future versions, refining the guidelines to address emerging technologies.

  • WCAG 1.0, released in 1999, established the first internationally recognized standards for web accessibility. It is now largely obsolete, following the publication of WCAG 2.0.
  • WCAG 2.0, released in 2008, brought significant improvements and introduced a more comprehensive approach to accessibility. It introduced a set of four principles: Perceivable, Operable, Understandable, and Robust (POUR) and success criteria for each guideline, providing clearer instructions for compliance.
  • WCAG 2.1, released in 2018, expanded upon WCAG 2.0. It primarily focused on mobile accessibility, low vision, and cognitive and learning disabilities. WCAG 2.1 is backward compatible with WCAG 2.0, meaning that conformance to WCAG 2.1 also satisfies the requirements of WCAG 2.0.

This guide focuses on the provisions of WCAG 2.0 regarding closed captions in online video. Since WCAG 2.1 contains no new provisions in this area, a WCAG 2.0 compliant captioning solution will also be WCAG 2.1 compliant.

Levels of Conformance

WCAG is structured into three levels of conformance: A, AA, and AAA. Level A represents the minimum level of accessibility compliance, while AA and AAA provide higher levels of accessibility. Each level builds upon the previous one.

Each guideline under WCAG 2.0 has a level of conformance assigned to it. Conformance to a specific level indicates the extent to which the guidelines have been implemented.

WCAG 2.0 provisions on closed captions

Video on-Demand and Live Streaming

WCAG 2.0 includes two guidelines related to closed captions.

  • For level A compliance, guideline 1.2.2 requires closed captions to be present in pre-recorded online video.
  • For level AA compliance, guideline 1.2.4 requires closed captions to be present in live streaming video.

To be WCAG compliant, captions should be accurate and synchronized with the audiovisual content.

Since WCAG aims to ensure accessibility for the hearing impaired, the captions should also include all relevant non-speech information in order to be accurate, such as sound effects, music and speaker identification.

No technical requirements

WCAG focus is on the provision of accurate and synchronized captions, without specifying the specific means of implementation. It doesn’t contain specifications on how captions should be rendered or displayed or prescribed captioning formats.

The website of the Web Accessibility Initiative (WAI) does provide a few general instructions for transcribing your own captions for the hearing impaired:

  • Captions are one or two lines. Generally it is best to keep them under 32 characters per line.
  • Put a new sentence on a new line.
  • If you need to break a sentence into multiple segments, break it at a logical phrase.

Note that these guidelines are NOT part of the WCAG itself. The WCAG also refers to Captioning Key and other best practices for online captioning, but this is for informational purposes only. It does not imply any endorsement.

No quality metrics

WCAG 2.0 contains no metrics for measuring the quality of captions. Therefore, it is also impossible to specify a percentage of accuracy that is required.

The W3C takes a broader approach to accessibility by requiring that captions, like all other Web content, must conform to each of the POUR principles:

  • Perceivable: information and user interface components must be presented in a way that can be perceived by all users, including those with visual or auditory impairments. For example, it should be possible to change the font and text size of the captions.
  • Operable: user interface components and navigation must be operable by all users, including those who may have mobility impairments. For example, viewers should be able to turn on the captions using their keyboard.
  • Understandable: the content and operation of the website should be clear and understandable to all users.
  • Robust: the website should be compatible with a wide range of user agents (browsers, assistive technologies, etc.) to ensure that all users can access the content.

Essentially, this means that the user experience should be similar for viewers with or without disabilities.

Other WCAG 2.0 provisions on video accessibility

In addition to the provisions requiring closed captions, WCAG includes other guidelines related to online video.

Provisions regarding online video

  • Guideline 1.2.1 (level A) requires that alternative text, which is a concise textual description, is provided for all pre-recorded videos.
  • Guidelines 1.2.3 (level A) en 1.2.5 (level AA) require an audio description for pre-recorded videos. An audio description is an additional audio track that describes the visual elements of the content, like actions, characters, scene changes… For level AA compliance this is required. For level A it may be replaced by a media alternative that is separate from the video (e.g. a text-based transcript or a separate audio track).
  • Guideline 1.2.6 (level AAA) requires that sign-language interpretation is available for all pre-recorded videos.
  • Guideline 1.2.7 (level AAA) requires an extended audio description in pre-recorded videos, when pauses in foreground audio are insufficient to allow the captions to convey the sense of the video.
  • Guideline 1.2.8 (level AAA) requires a media alternative in text form for all pre-recorded videos. This is for individuals whose vision is too poor to reliably read captions and whose hearing is too poor to reliably hear the audio.

General provisions, applicable to online video and closed captions

  • Keyboard accessibility (Guideline 2.1, level A) requires that all video controls and interactive elements can be accessed and operated using a keyboard alone, without relying on a mouse or other pointing device.
  • Contrast (Guideline 1.4, level A): ensuring sufficient color contrast between video elements and their backgrounds is essential for users with low vision or color vision deficiencies.

Adoption of WCAG in international legislation

When it comes to online video, WCAG 2.0 Level AA is currently considered as the industry standard.

Some form of the WCAG has been adopted in many countries, mostly for (part of) the public sector. For example:

  • In the United States, section 508 of the Rehabilitation Act has adopted WCAG 2.0 Level AA for websites of federal agencies. Many states have extended this to (certain) federally funded organizations.
  • The Web Accessibility Directive (Directive (EU) 2016/2102) of the European Union requires public sector websites and mobile applications within the European Union to conform to the Web Accessibility Directive, which is closely related to WCAG 2.0 Level AA. Many EU countries have also adopted their own web accessibility laws that incorporate WCAG 2.0.
  • The UK’s Equality Act of 2010 uses WCAG 2.0 as the standard for websites in the public and private sector.
  • Japan’s JIS X 8341 is based on WCAG 2.0 criteria and is required for all local and central government websites. Commercial websites can voluntarily comply.
  • Isreal’s non-discrimination law requires public and private sector entities to meet WCAG 2.0 Level AA standards.
  • In countries like Canada, Brazil and India, a mandatory policy requires government agencies to meet WCAG 2.0 Level A criteria.