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Multimedia Accessibility


Captions are text versions of the spoken word presented within multimedia. Captions allow the content of web audio and video to be accessible to those who do not have access to audio. Though captioning is primarily intended for those who cannot hear the audio, it has also been found to help those that can hear audio content, those who may not be fluent in the language in which the audio is presented, those for whom the language spoken is not their primary language, etc.

Common web accessibility guidelines indicate that captions should be:

  • Synchronized - the text content should appear at approximately the same time that audio would be available
  • Equivalent - content provided in captions should be equivalent to that of the spoken word
  • Accessible - caption content should be readily accessible and available to those who need it

Captions as typically seen on television
Screenshot of black and white news footage showing battleships in the distance. Captions display on the image which read - the curtain rises on the greatest military experiment ever undertaken.

Captions can be either closed or open. Closed captions can be turned on or off, whereas open captions are always visible.

Television closed captioning is used by millions of individuals who are deaf or hard of hearing; millions more use it in the classroom or in noisy environments—like bars, restaurants, and airports. As the average age of the population increases, so does the number of people with hearing impairments.

Captions as seen in a web media player
Screenshot of captions in a web media player

Open captions are similar to, and include the same text, as closed captions, but the captions are a permanent part of the video picture, and cannot typically be turned off. Open captions are not decoded by the television set, but are a part of the video information. This typically requires a video editing or encoding program that allows you to overlay titles onto the video. The captions are visible to anybody viewing the video clip and cannot be turned off.

For web video, captions can be open, closed, or both. Closed captions are most common, utilizing functionality within video players and browsers to display closed captions on top of or immediately below the video area.

Audio Descriptions

Audio descriptions are intended for users with visual disabilities. They provide additional information about what is visible on the screen. This allows video content to be accessible to those with visual disabilities. Audio descriptions are helpful on the web if visual content in web video provides important content not available through the audio alone. An example of audio descriptions for something you have probably seen and heard is found below. Can you visualize what is being described?

Listen to Audio Descriptions in MP3 Format (152KB)

If web video is produced with accessibility in mind, then audio descriptions are often unnecessary, as long as visual elements within the video are described in the audio.