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What are captions? | Nomensa

What are captions?

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2 minutes, 12 seconds

Everybody’s using YouTube. Government departments, media corporations and individuals with bright ideas all broadcast themselves. YouTube might be everywhere, but is your content reaching everyone? Knowing about audio description, captions and transcripts, is the way to reach an even wider audience. In the third of a series of articles on multimedia accessibility, we take a look at captions.



Captions are a text based alternative to multimedia content. The spoken dialogue and sound effects from the original soundtrack are displayed on screen in real time as the video plays. Captions can either be open or closed. Open captions are always visible on screen, where as closed captions can be enabled only when they’re needed by the person watching your multimedia content.


Who benefits from captions?

Deaf and hearing impaired people benefit most from captions. It’s also possible that people in a noisy environment, or stuck without speakers may also find them useful, but that’s more of a happy side effect than anything.


WCAG 2.0 success criteria

There are two success criteria under the Web Content Accessibility Guidelines 2.0 that deal with captions:


    • 1.2.2 Prerecorded media;
    • 1.2.4 Live media.


1.2.2 Prerecorded media

This success criterion deals with prerecorded audio/video multimedia. If you broadcast prerecorded content on your website, you’ll need to provide either open or closed captions to meet this Level A checkpoint.

1.2.4 Live media

This Level AA success criterion is similar to 1.2.2, except that it deals with live audio/video content. If you stream live broadcasts from your website, you’ll need to provide either open or closed captions along with it.


When should captions be used?

The success criterion above cover both prerecorded and live broadcasts. In other words, if you’re broadcasting any kind of audio/video content on your site, you’ll need to think about captions.


Creating captions

Captions are effectively time coded transcripts (we covered transcripts in a previous article). The time coding enables the captions to be synchronised on screen with the original soundtrack as the video plays. Captions can be created using different technologies. Nomensa’s accessible media player uses XML to format captions. Another common option is SMIL. When it comes to creating captions, YouTube has a useful feature that makes it a little bit easier. When you upload your video you can upload a transcript and YouTube will use speech recognition technology to create the captions for you. The only proviso is that your YouTube transcript must be in English. Also worth bearing in mind that speech recognition isn’t the most precise of technologies, so check your captions carefully before you broadcast!

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