2. Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation. (508:B. W3C: 1.4 Priority 1)
Auditory presentations must be accompanied by text transcripts, textual equivalents of auditory events. When these transcripts are presented synchronously with a video presentation they are called captions and are used by people who cannot hear the audio track of the video material.
Some media formats (e.g., QuickTime 3.0 and SMIL) allow captions and video descriptions to be added to the multimedia clip. SAMI allows captions to be added. The following example demonstrates that captions should include speech as well as other sounds in the environment that help viewers understand what is going on.
Example.
Captions for a scene from "E.T." The phone rings three times, then is answered.
[phone rings]
[ring]
[ring]
Hello?"
End example.
Until the format you are using supports alternative tracks, two versions of the movie could be made available, one with captions and descriptive video, and one without. Some technologies, such as SMIL and SAMI, allow separate audio/visual files to be combined with text files via a synchronization file to create captioned audio and movies.
Some technologies also allow the user to choose from multiple sets of captions to match their reading skills. For more information see the SMIL 1.0 ([SMIL]) specification.
Equivalents for sounds can be provided in the form of a text phrase on the page that links to a text transcript or description of the sound file. The link to the transcript should appear in a highly visible location such as at the top of the page. However, if a script is automatically loading a sound, it should also be able to automatically load a visual indication that the sound is currently being played and provide a description or transcript of the sound.
Note. Some controversy surrounds this technique because the browser should load the visual form of the information instead of the auditory form if the user preferences are set to do so. However, strategies must also work with today's browsers.
What are considered equivalent alternatives?
Captioning for the audio portion and audio description of visual information of multimedia presentations are considered equivalent alternatives.
This provision requires that when an audio portion of a multimedia production is captioned, as required in provision (a), the captioning must be
synchronized with the audio. Synchronized captioning would be required so someone reading the captions could also watch the speaker and
associate relevant body language with the speech.
If a website offers audio files with no video, do they have to be captioned?
No, because it is not multimedia. However, since audio is a non-text element, a text equivalent, such as a transcript, must be available. Similarly,
a (silent) web slide show presentation does not need to have an audio description accompanying it, but does require text alternatives to be
associated with the graphics.
PowerPoint
If there is a slide show like a PowerPoint slide show available but it is "visual only",
the graphics need to have alternative text representations. For those providing silent Microsoft PowerPoint
presentations via the Internet can do this by following the steps below:
- Select the Image that needs alternative text
- Select Format|Format Picture from the Main Menu
- Select the "Web" tab
- Type in the Alternative Text
- Click on OK
