Audio and Video presentations

Audio

Audio content presents two, different, problems with regard to accessibility.

  1. Deaf people (and anyone without a working speaker or earphones) cannot hear the audio.
  2. Blind people can hear the audio, but it drowns out their screen reader audio so that they cannot hear the screen reader instructions. This stops them doing anything else until the audio stops !

The solutions are

  1. provide a text transcript of the audio content for deaf people to read
  2. make sure that your audio does not start automatically but only activates when the user selects a play button.
  3. You should also indicate how long the audio lasts. For example - To play the prime minister's speech (duration 5.5 minutes) select the play the speech link. To stop the speech at any time press the Escape button on your keyboard <a href="/myaudio.wmv">Play the speech</a>

If you want to make a sound when a page loads please ensure that it does not last for more than 3 seconds. You can let your audience select to hear the sound again, but make sure that they have the choice.

Video

Video adds real value to a website. As technologies improve and more people have access to broadband we can expect to see more and more video content on the web. Video presentations normally have an audio track, so the problems for audio described above need to be addressed here as well. In addition, the video images are not available to blind people, so if this is important you will need to include visual instructions with the transcript. If the video is just "talking heads" (e.g. a speech) subtitles or transcripts are probably sufficient. But if the video is a demonstration then the instructions need to be described in text form so that blind people and deaf people can understand what is going on.

Providing a text based alternative is fairly easy to do and it is the only universal solution. If you are demonstrating how to cook a chicken you just provide a link to a page that gives the recipe and cooking instructions in text form. Providing subtitles, audio descriptions of the video action, signing or other supporting technologies makes your video more inclusive, but these technologies must not be used at the expense of providing a good text based alternative.

Including sign language with a video presentation

Signing (simultaneous presentation by someone using sign language) is a "nice to have" addition to any video. But it is not essential and should only be considered if all other accessibility issues have been addressed (and you have a generous budget). If you do decide to add signing you will need to know which sign language your intended audience uses. There are a number of variations, English, American, Irish and so on. Even in UK not everyone prefers the British version (BSL), some use a version called Makaton.

Embedding the video

Videos are normally “embedded” into a page using the <embed> element. For users who do not have the facility to view videos please provide a <noembed> alternative immediately after the closing </embed> element. This might look like this

<embed>
-- Video details go here --
<noembed>
<p>This video shows how to cook a chicken on an open fire. For a text version of these instructions please select the following link <a href=”chickentext.html”>how to cook a chicken</a></p>
</noembed>
</embed>

For less common media players it is best to offer a link to the video or application on a seperate page rather than embeding it in the current page so that the user has the choice as to whether to install the relevant player or to ignore the video.

Synchronising alternative text presentations

For archived multimedia

Multimedia (video and audio combined) files that are uploaded to your server and made available for people to see or hear at any time need to have the subtitles available to match the video content so that deaf people can follow the story line. Video only and audio only files do not need to have their text alternative versions synchronised, just make sure that they present the same information.

For live streaming multimedia

Live streaming, or anything that requires the user to react at a particular time, must have the subtitles (text alternative) available at the same time as the audio so that a deaf person is not penalised.

These are advanced techiques and are not covered further in this set of lessons.


Lesson Summary

  1. Do not rely on javascripts, always provide an HTML alternative for any script that persorms an action
  2. Design javascripts to work with the keyboard as well as the mouse
  3. Always provide a means to void loading a Flash animation
  4. Provide an HTML alternative to any animations
  5. Provide a text alternative to any audio such as speeches
  6. Do not let audio start automatically (unless it is less than 3 seconds)
  7. Provide accessible controls for any audio so that the user can stop or pause the audio
  8. Provide a text transcript for any video
  9. Provide sub-titles for video
  10. Provide accessible controls for any video so that the user can stop or pause the video

Resources

Adobe Accessibility Resource Centre http://www.adobe.com/accessibility/index.html

W3C evaluation of Real Player (http://www.w3.org/WAI/UA/implementation/eval_win_real6.html) and windows media player (http://www.w3.org/WAI/UA/implementation/eval_win_mediaplayer8.html).