EPUB 3 Accessibility Guidelines

Video

When including video clips, ensure that the native reading system controls are enabled by default. If a reading system supports custom controls, the native controls can be disabled by the JavaScript code.

The following methods for making video content accessible are recommended in the HTML5 specification:

Although the video element allows child content for fallback purposes, such content is not intended to serve as an accessible alternative (it is only made available to the reader if video is not supported by the reading system).

The video element also includes the poster attribute to allow a default image to be set for display while no data is available. This image can also serve as a fallback in EPUB publications when video, or the video format, is not supported. There is currently no way to describe this image, however, so text fallbacks should be preferred. (Discussions are ongoing in the HTML5 Working Group to find ways to redress the problem of video being supported and the poster image conveying additional information of interest to the reader.)

Agreement on universal support for a video codec and container could not be reached in HTML5, and is a similar issue for EPUB 3. Although the EPUB 3 specification technically allows any format (without fallback), the IDPF recommends one or both of the following formats be included:

While this might not seem like an accessibility issue, consider that it means that many more readers might be relying on fallbacks than you might at first anticipate.

Examples

Example 1 — Including a video using the src attribute
<video
       src="video/the_general.webm"
       controls="controls">
   …
</video>
Example 2 — Including more than one video option using the source element
<video controls="controls">
   <source
           src="video/the_general.webm"
           type="video/webm"/>
   <source
           src="video/the_general.mp4"
           type="video/mp4"/>
   …
</video>
Example 3 — Including timed tracks
<video controls="controls">
   <source
            src="video/the_general.webm"
            type="video/webm"/>
   <source
            src="video/the_general.mp4"
            type="video/mp4"/>
</video>
Example 4 — Including a poster image
<video
       src="video/the_general.mp4"
       poster="graphics/the_general.jpg"
       controls="controls">
   …
</video>
Example 5 — Including a fallback error message
<video
       src="video/the_general.mp4"
       controls="controls">
   …
   <div class="err">
      <p>
         Sorry, it appears your system 
         either does not support video 
         playback or cannot play the 
         MP4 format provided.
      </p>
   </div>
</video>

Compliance References and Standards

Additional Resources