# Understanding Time-Based Media

## Intent of Time-Based Media

The purpose of this guideline is to provide access to time-based and synchronized media.This includes media that is:

- audio-only
- video-only
- audio-video
- audio and/or video combined with interaction

To make it easy for authors to quickly determine which success criteria apply to their content, the type of media each success criterion applies to is included in its short name.

For audio-only or video-only media, you only need to apply the success criteria that say " audio-only" or " video-only" in their short name. If your media is not audio-only or video-only, then all the rest of the success criteria apply.

Media can also be live or prerecorded. Each of the success criterion short names clearly tells you if the success criterion applies to live or prerecorded media.

Synchronized media is defined in the glossary as:

Note that an audio file accompanied by interaction is covered here, as is a video-only file that involves interaction. These are covered because interaction must take place at a particular time. Having a text transcript that said, "for more information, click now," would not be very helpful since the reader would have no idea when the audio said, "now." As a result, synchronized captions would be needed.

Sometimes, there is so much dialogue that audio description cannot fit into existing pauses in the dialogue. The option at Level A to provide an alternative for time-based media instead of audio description for synchronized media would allow access to all of the information in the synchronized media. This option also allows access to the visual information in non-visual form when audio description is not provided for some other reason.

For synchronized media that includes interaction, interactive elements (for example links) could be embedded in the alternative for time-based media.

This guideline also includes (at Level AAA) sign language interpretation for synchronized media as well as an approach called extended audio description. In extended audio description, the video is frozen periodically to allow more audio description to take place than is possible in the existing pauses in the dialogue. This is a case where higher-level Success Criteria build upon the requirements of lower-level Success Criterion with the intention of having cumulative, progressively stronger, requirements.

### Additional Techniques (Advisory) for Time-Based Media