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Web Accessibility: Multimedia

§1194.22 (b) Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation.

§1194.22 (m) When a web page requires that an applet, plug-in or other application be present on the client system to interpret page content, the page must provide a link to a plug-in or applet that complies with 1194.21(a) through (l).

The term “Multimedia” covers audio, video, and animation. In terms of accessibility these fall into the categories: Providing audio descriptions of movies and animations for visually impaired users and; Providing captioning for users with hearing loss. In either case a separate transcript could be supplied describing the media but the realtime solutions are preferred. These are discussed on the rest of this page.

Accessible Audio

Audio can be made accessible simply by providing a transcription. Such transcriptions should also include descriptions of audio cues as well, such as "laughter" or "applause". The preferred method is to include the full transcription on the web page with the audio. This makes a lot of sense when the audio is primarily spoken word, as it not only makes the presentation accessible to those with hearing loss but it also provides the added possibility of searching and indexing the presentation. If including the full transcription on the page or as a longdesc is undesirable then you can supply a link to the transcription.

Accessible Video

Supporting Impaired Vision Users

The first thing to consider when adding support for blind users to your videos and animations is to simply add a descriptive audio track to the work. In cases where there is already an audio track it must be evaluated to ascertain whether or not it is sufficiently descriptive on its own. If it isn't then descriptive text must be integrated onto the page, provided in a longdesc, or supplied through a link.

Supporting Users with Hearing Loss

Support for hearing impaired users comes down to two main applications: Audio recordings and videos (including animations). In general, audio recordings can be made accessible simply by providing a transcript.

The best way to make videos accessible is to provide captioning. Captioning comes in two types, open and closed. Open captioning is always visible and can't be turned off. Closed captioning is visible when the user wants it. Closed captioning on the broadcast channels has been required by law in the United States for many years. To meet Section 508 requirements captioning must 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

Unlike other aspects of accessible web design, captioning requires use of additional technologies, and therefore choices, by the web developer. First, there is a choice as to what format to use for the media. QuickTime and Flash they are common choices because they support closed captioning. Second is choosing the method of captioning. There are many third-party solutions available that aid the captioning process, though they require some time to get to know how they work. The third choice is which captioning protocol to use. There are several of these, and your choice will likely depend on the format preferred by the software you use to caption your videos.

The easiest and cheapest way for the novice to caption videos is to upload them to YouTube and, using YouTube's Captions and Subtitles panel, request processing via Machine Transcription. In order for this to work the spoken audio must be clear enough for the machine transcription to provide a reasonably accurate transcription. Once this is done you can download the transcription to edit it, then upload it to YouTube again to have it installed as a closed caption.

There are many ways of creating transcriptions, of course. The example below was processed using a Mac application called "MovCaptioner" to produce a SubViewer format captioning file. This was then uploaded using YouTube's Captions and Subtitles panel to add the closed captioning to it.

Note: As always, when putting movies on the web you must try to choose a format that will be usable by the greatest number of users. Though YouTube is very popular it requires the Flash browser plug-in. If this is a problem for your user base then you may have to find another format that supports captioning, and learn how to use the tools that go with it.

Captioning Resources

General Information

http://jimthatcher.com/webcourse6.htm

http://www.webaim.org/techniques/captions/

YouTube: Adding and Editing captions

Tools and Techniques

WebAim: Hi Caption

QuickTime Pro Closed Caption Importer: http://developer.apple.com/mac/library/samplecode/ClosedCaptionImporter/

Adding closed captioning to a QuickTime movie: http://ncam.wgbh.org/invent_build/web_multimedia/mobile-devices/m4v-captions

How to use MovCaptioner (Mac only): http://www.youtube.com/watch?v=yh3UegeqZeQ