Captions are provided for prerecorded audio content in synchronized media, except when the media is a media alternative for text and is clearly labeled as such.


Rationale

The purpose of this checkpoint is to enable deaf people and people with hearing impairments to access audio portions of multimedia. Captions are text on the screen that identify speakers, dialogue, music, and sound effects. Captions fall into two types:

Required development and unit test techniques


To comply with this checkpoint, you must meet at least one of the following techniques.

  1. Open captions: Provide open (always visible) captions.
  2. Closed captions: Provide closed captions.

Note: The examples presented in the techniques are not exhaustive. They are meant to illustrate the spirit of this checkpoint.

General examples

  1. Open captions: Provide open (always visible) captions.

    To comply with this technique, you must implement the following example.

    General example 1

    Open captions are embedded into the multimedia presentation. The captions are burned into the video image and users cannot turn them off. The advantage to this type of captioning is that additional software or technology is not needed to view the captions. The open captions can be placed on any video stream, regardless of whether or not the technology supports closed captioning. The disadvantage of open captions is that users do not have the ability to turn them off, so users without visual or hearing impairments will see the dialogue in addition to hearing it from the audio track.

    An example of captions embedded into the video stream is shown in the screen shot below. As the captions run automatically when the video is playing, the user does not have the option of turning off the captions.

    That brings the voice of the internet to to blind and visually impaired users.

    For additional information, refer to the WCAG 2.0 examples of providing open captions (link resides outside of ibm.com).

    Required unit tests for general development technique 1

    Manually perform the following unit tests.

  2. Closed captions: Provide closed captions.

    To comply with this technique, you must implement the following example.

    General example 2

    Closed captions are usually created as a stream of data that runs in parallel with the multimedia. A user can turn these captions on or off. Closed captions must be provided using any readily available media format that has a video player, is free of charge and supports closed captioning.

    Note for iOS platform: Mobile Safari does not support third party plug-ins or applets that display video. Therefore, use the HTML5 video element to display video on an iOS device and follow Apple's guidance for creating captioned video.

    An example of a multimedia presentation that contains captions is shown in the screen shot below. The "cc" button at the bottom of the screen allows the user to turn the captions on or off.

    IBM Accessibility Services

    You can use SMIL 1.0 and SMIL 2.0 to create closed captions for a variety of different media players. For a detailed list of players that support SMIL 1.0 and SMIL 2.0, refer to the W3C Synchronized Multimedia (link resides outside of ibm.com) page.

    For additional information, refer to the WCAG 2.0 examples of providing closed captions (link resides outside of ibm.com).

    Required unit tests for general development technique 2

    Manually perform the following unit tests.


Adobe® Flash® examples

For techniques that have no Flash-specific examples, refer to the general examples for guidance.

  1. Open captions: Provide open (always visible) captions.

    There are no specific examples for implementing this technique in Adobe® Flash®. Use the general examples as a guide.

  2. Closed captions: Provide closed captions.

    To comply with this technique, you must implement the following example.

    Flash example 1

    For movie clips and other meaningful Flash objects, include a full description of the action taking place in the clip. Do not rely on subtitles only because they do not adequately describe all of the action on the screen. In addition, provide audio playback controls so that users can control the speed, volume, and navigation of audio clips. Review Checkpoint 2.1a Keyboard Functionality to ensure that all controls are keyboard accessible.

    Required unit tests for Flash development technique 2

    Refer to the required unit tests for general development technique 2.

Note for iOS platform: Mobile Safari does not support Java applets, Flash or other third party plugins. Therefore, equivalent content must be presented in a manner that is accessible on iOS devices. Apple recommends using the HTML5 audio and video elements for audio and video content. However, these elements use the browsers' native players, and the controls on the players are not keyboard accessible. Therefore, developers must use the HTML5 audio/video API, JavaScript and CSS to implement keyboard focusable controls. An example implementation of an accessible HTML5 video/audio player can be found in chapter 6 of Pro HTML5 Accessibility: Building an Inclusive Web (link resides outside of ibm.com).


Recommended development techniques

Although you do not have to implement the following recommended techniques in order to comply with this checkpoint, you should review them because they can improve the accessibility and usability of the application.

  1. Ensure your captions adhere to the standard captioning guidelines.
  2. Provide a note stating "No sound is used in this clip" for video-only clips.
  3. Use SMIL 1.0 to provide captions for all languages present in the audio tracks.
  4. Use SMIL 2.0 to provide captions for all languages present in the audio tracks.
  5. Provide a pop-up text window for a short audio presentation.

Recommended development technique 1 examples

Ensure your captions adhere to the standard captioning guidelines. For example:

Note: The examples for recommended development techniques 2-6 are currently under development by the WCAG 2.0 Working Group.


©2013 IBM Corporation

Last updated January 1, 2013.

W3C Recommendation 11 December 2008: http://www.w3.org/TR/WCAG20/ (link resides outside of ibm.com)
Copyright 1994-2009 W3C (Massachusetts Institute of Technology, European Research Consortium for Informatics and Mathematics, Keio University), All Rights Reserved.