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:
The track element can be used to include subtitles, captions and descriptions.
Subtitles and captions can be embedded directly in the video.
The track element can be used to provide navigation by scene (the chapters track type).
A link to a transcript can be provided.
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:
H.264
WebM
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.
<video
src="video/general.mp4"
controls="controls">
…
</video>
<video controls="controls">
<source
src="video/general.mp4"
type="video/mp4"/>
<source
src="video/general.webm"
type="video/webm"/>
…
</video>
<video controls="controls">
<source
src="video/general.mp4"
type="video/mp4" />
<track label="Norsk" kind="subtitles" srclang="no" src="video/subtitles/vtt/general.vtt" default />
</video>
<video
src="video/the_general.mp4"
poster="Images/general.jpg"
controls="controls">
…
</video>
<video
src="video/general.mp4"
controls="controls">
…
<div class="err">
<p>
MP4-formatet kan ikke spilles av.
</p>
</div>
</video>
Compliance References and Standards
HTML5 — The video element
HTML5 — The track element
WCAG 2.0 — G19: Ensuring that no component of the content flashes more than three times in any 1-second period
WCAG 2.0 — G78: Providing a second, user-selectable, audio track that includes audio descriptions
WCAG 2.0 — G87: Providing closed captions
WCAG 2.0 — G93: Providing open (always visible) captions
Additional Resources
The Definitive Guide to HTML5 Video, Sylvia Pfeiffer (Apress)