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How To Audio and Video Topics: Accessible File Types | Transcripts | Captions | Audio Descriptions

Students Affected:

Principles: Provide Meaningful Alternatives

What It Means

An audio description is a verbal statement of the on-screen visuals, usually inserted between dialogue. For example, the dialogue might consist of a character stating, "I'm king of the world!" and the audio description—spoken by a different, neutral voice—would say, "He stands on the bow of the ship, arms outstretched."

Example The Able TV Web site includes a sample video with audio description (requires RealOne Player).

If You Do It Wrong: A student who is blind misses any visual actions, on-screen text, or changes of scene.

If You Do It Right: Audio descriptions let listeners picture the scene correctly in their heads, making it easier to understand the video.

How It Works

1. Create an audio track that describes any visual content. This track is typically inserted during breaks in the dialog, so the descriptions should be relatively short. If the descriptions are longer than the breaks, you may have to momentarily pause (freeze) the presentation while video content is described audibly.
   
   
2. Synchronize the audio description with the video. The audio description can be added during editing as an alternate audio track in some video file formats. You can also use a complex Synchronized Multimedia Integration Language (SMIL) or Microsoft Synchronized Accessible Media Interchange (SAMI) file, which can be set to pause the main presentation at a specific place, play another audio file (the description), then continue playback of the main presentation.

You might want to maintain two versions of the video—a described version for students who are blind, and an undescribed version for students who do not need an audio description.

The WGBH Media Access Group Description Video Service creates audio descriptions for television shows, movies, and other types of video. To learn how to create audio descriptions, visit the NCAM Rich Media Web site. Two helpful pages are Creating Audio Descriptions for Rich Media and Access Strategies: Audio Description.

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