Audio Descriptions
Audio descriptions are much easier to implement than they are to create. These are carefully written to narrate key visual elements, and are then recorded and inserted during pauses in dialog. The descriptions are more challenging to create than captions. While captions are written based on sounds and speech, audio descriptions are an interpretation of visual events, which must be worded so that the recorded version will fit into available pauses. Descriptions must be objective, providing enough information that the user can form his or her own interpretation. Professional description services are available and should be considered as a budget item for large, real time, and high visibility projects.
Audio Description Tools And Strategies
Apart from hiring professional services, few options exist for creating audio descriptions. Because audio descriptions fit into pauses in dialog, it's crucial to know when to start the description and how long it can last. You can quickly record audio descriptions at a workstation using basic sound-editing software, but results improve significantly with a more sophisticated set-up, time, and training.
| Example 3 |
<par dur="0:01:46.27">
<video dur="0:01:46.27"
region="videoregion" src="mymovie.mov"/>
<audio begin="0:00:14.30" src="ad1.wav"
systemAudioDesc="on"/>
<audio begin="0:00:28.16" src="ad2.wav"
systemAudioDesc="on"/>
.
.
</par>
|
| This SMIL file contains references to the audio description sound files. |
MAGpie 2.01 can record and synchronize audio descriptions. When exporting a described presentation for RealPlayer and QuickTime, MAGpie creates a SMIL file that contains references to the audio description sound files. See Example 3 for sample code. The systemAudioDesc test attribute is used to determine whether the player is set to play an audio description. (QuickTime ignores this test attribute.)
Some video clips have no pauses in the dialog or breaks in the action where descriptions might be placed. A new feature in SMIL 2.0 lets you add audio descriptions to a video clip where pauses are nonexistent or insufficient for adequate description. The exclusive tag (<excl>) informs the player that the main media (and other tracks, if applicable) should be paused until the interrupting element has finished playing. This has the effect of lengthening the overall duration of the presentation, but provides a possible avenue for adding description when it is most needed. Example 4 shows sample code for extended audio description, where the video is temporarily paused while ad1.rm and then ad2.rm play.
You can add audio descriptions to a presentation in the RealPlayer using SMIL, as shown in Example 4. QuickTime lets you add audio descriptions in the same way as caption files, by adding the description files to the movie with QuickTime's authoring features or by creating a SMIL file. However, QuickTime doesn't yet support the <excl> tag, so extended audio description in QuickTime must be implemented using the QuickTime authoring features. Windows Media has no official support for audio descriptions, but you add audio description by combining the audio description with the video and program audio while encoding to a Windows Media file type.
| Example 4 |
<excl>
<priorityClass peers="pause">
<video src="movie.rm" region="video"
title="video"/>
<audio src="ad1.rm" begin="12.85s"
systemAudioDesc="on"/>
<audio src="ad2.rm" begin="33.71s"
systemAudioDesc="on"/>
</priorityClass>
</excl>
|
| Sample code for extended audio description. The video pauses temporarily while a description catches up. |
When delivering high bandwidth media for blind and visually impaired users, providers can offer options that will save bandwidth on both ends. Users who are blind have no use for the video, only the program audio and audio descriptions. Users who
are visually impaired may be able to use a screen magnifier to view some aspects of the video, but still benefit from audio descriptions. Sighted users have no need for the audio descriptions. To deliver the smallest amount of necessary material, your presentation can offer separate links representing these three possibilities. When using a RealServer, the systemAudioDesc test attribute controls audio description streaming, but a separate link to a
"no video" version is still necessary.
Additional Benefits of Audio Descriptions
As with captions, audio descriptions have additional benefits that increase their appeal. Because descriptions usually exist in text prior to being recorded, you can use the data for indexing video. Caption and description data can be held in XML documents and repurposed to create collated caption and description text files as an alternative for people with low bandwidth connections or who are viewing content through a small device like a cell phone. This approach also helps people who are both deaf and blind and need to convert all information into Braille. Audio descriptions also offer benefits for users who aren't blind. Descriptions are used as an additional mode of accessing information to help people with cognitive and learning disabilities reinforce concepts introduced in video. They can also be used in settings where only audio is available.
What's Next?
Support for audio description and extended audio description isn't as good as it should be in many players. Screen readers must have better access to player content before people who are blind or visually impaired will be able to fully access streaming content. Support for captions is adequate for basic text display, but support for captions that overlap video and for sophisticated text, such as mathematical equations, needs work.
A W3C task force recently began to examine the need for a caption format that all players can support. Improvements in speech-to-text technology are also on the wish list, with the goal being automated captioning. Speech-to-text conversion tools will undoubtedly be commonplace before automated captioning, but they'll assist caption writers and help streamline the work process.
Captions and audio descriptions are workable solutions for providing access to streaming content. While governmental content providers must add these enhancements, there is no such legislative mandate for the private sector yet. However, even if there are no legal reasons to provide accessible content, streaming companies can benefit from doing so. Accessible sites engage potentially millions of new users, and additional textual information adds value to services, which certainly never hurts the bottom line.
Andrew ([email protected]) manages the Access to Rich Media project at the CPB/WGBH National Center for Accessible Media.
