If any audio on a Web page plays automatically for more than three seconds, either a mechanism should be available to pause or stop the audio, or a mechanism should be available to control audio volume independently from the overall system volume level.
To provide the best clarity of sound for audio, exclude background sounds from foreground speech. Give users the options to turn off background sounds when possible. Background sounds should be four times quieter (20 decibels lower) than foreground sounds.
Flash, QuickTime, or Windows Media Player video with sound must include captions in sync with the video.
If audio sound is a decoration, captions can indicate the sound is occurring. For instance, closed captioning indicates music with music note symbols.
Users who cannot hear should be able to access real-time synchronized media broadcasts through real-time captions.
A sensory experience could be a video that is not purely decorative and does not primarily convey important information or perform a function. An example would be a performance of a flute solo. Text alternatives such as a long description, alt text or a simple text description before or after the sensory experience can provide descriptive identification of the non-text content.
Including a text file, known as a transcript, of audio or video is acceptable only for audio or video that is prerecorded and not streaming live.
Video without sound must have an audio description or transcript.
The guidelines listed below are not required but would be best case scenarios for Web accessibility. Due to bandwidth issues, budget and time constraints the guidelines below may not be followed.
A synchronized media presentation involves creating a document that tells the story of a visual presentation. It includes all the important dialogue and actions as well as descriptions of backgrounds etc. that are part of the story.
Here is an example video of a synchronized media presentation.
For those who communicate primarily in sign language it is sometimes less preferable and sometimes not possible for them to read and understand text at the rate it is presented in captions. For these individuals it is important to provide a sign language presentation of the audio information. One universally compatible way to provide sign language is to simply embed a video of the sign language interpreter in the video stream.
Note 1: If the video stream is too small, the sign language interpreter will be indiscernible. When creating a video stream that includes a video of a sign language interpreter, make sure there is a mechanism to play the video stream full screen. Otherwise, be sure the interpreter portion of the video is adjustable to the size it would be had the entire video stream been full screen.
Note 2: Since sign language is not usually a signed version of the printed language, the author has to decide which sign language to include. Usually the sign language of the primary audience would be used. If intended for multiple audiences, multiple sign languages may be used.