When including video clips, ensure that the native reading system controls are enabled by default (i.e.,
by setting the
controls attribute on the
video element). This practice ensures
that the control are accessible even if scripting is not available. If custom controls are provided and
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 the
video element is not supported by the reading system, which typically only occurs in
EPUB 2 reading systems.
The following methods for making video content accessible are instead recommended in the HTML5 specification:
trackelement to include subtitles, captions and descriptions.
trackelement (i.e., using the
video element also includes the
poster attribute to allow a default image to
be set for display while no data is available. There is currently no way to describe this image, however,
so text fallbacks should be preferred.
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 MP4 and WebM 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.