Guide to Guideline 1.2 Level 3 Success Criterion 2

Key terms and important concepts

extended audio descriptions

In cases where a longer audio description is necessary but there is not a sufficient pause in the audio to accommodate it, the audio and video are paused while the audio and description plays. When the description has finished playing, the video and dialog resume playback. Extended and "regular" descriptions may be mixed in a single multimedia presentation.

multimedia

For the purposes of these guidelines, multimedia refers to combined audio and video presentations. It also includes audio-only and video-only presentations that include interaction.

Intent of this success criterion

The intent of this success criterion is to provide people who are blind or vision impaired access to a multimedia presentation. The extended audio description augments the audio portion of the presentation with the information needed when the video portion is not available.

Techniques for addressing 1.2 L3 SC2

The following combinations of techniques are deemed to be sufficient by the WCAG Working Group for meeting success criterion 1.2 L3 SC2.

Use a technology-specific technique to create an extended audio description for the multimedia content AND @@do we need conditions or discussion on how to write good extended audio descriptions?

Technology-Specific Techniques for 1.2 L3 SC2

Extended Audio Descriptions in SMIL 1.0

Provide audio descriptions that pause the timeline of the main media.
Video with audio descriptions that pause the main media.
```
<body>

  <par>
   <seq>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="0s" clip-end="5.4" 
       dur="8.7" fill="freeze"/>   
       <audio src="no1.wav" begin="5.4"/>
     </par>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="5.4" clip-end="24.1" 
       dur="20.3" fill="freeze"/>
       <audio src="no2.wav" begin="18.7"/>
     </par>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="24.1" clip-end="29.6" 
       dur="7.7" fill="freeze"/>
       <audio src="no3.wav" begin="5.5"/>
     </par>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="29.6" clip-end="34.5" 
       dur="5.7" fill="freeze"/>
       <audio src="no4.wav" begin="4.9"/>
     </par>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="77.4"/>
     </par>

   </seq>
  </par>
      
</body>
```
The markup above is broken into five <par> segments. In each, there is a <video> and an <audio> tag (the last <par> has no <audio> tag intentionally). The convention with extended audio desciptions is that the main media pauses during the description. The way to make this happen in SMIL 1.0 is to set a "clip-begin" and "clip-end" which dictate the start and end of the video clip, and to set a duration for the clip that is longer than what is defined by the "clip-begin" and "clip-end". The fill="freeze" holds the last frame of the video during the extended description. The <audio> tag has a "begin" attribute with a value that is equal to the "clip-end" value of the preceeding <video> tag.

The way to determine the values for "clip-begin", "clip-end", and "dur" is to find out the time the portion of the video before the audio description starts and ends, and to find out the total length of the extended audio description. The "clip-begin" and "clip-end" define their own values, but the "dur" value is the sum of the length of the extended description and the clip defined by the "clip-begin" and "clip-end". In the first <par>, the video clip starts at 0 seconds, ends and 5.4 seconds, and the description length is 3.3 seconds, so the "dur" value is 5.4s + 3.3s = 8.7s.

Extended Audio Descriptions in SMIL 2.0

Provide an extended audio description with the video track.

Video with extended audio description.

<smil xmlns="//www.w3.org/2001/SMIL20/Language">

<head>
   <layout>
     <root-layout backgroundColor="black" height="266" width="320"/>
     <region id="video" backgroundColor="black" top="26" left="0" height="144" width="320"/>
   </layout>
</head>

<body>	
   <excl>
     <priorityClass peers="pause">
       <video src="movie.rm" region="video" title="video"/>
       <audio src="desc1.rm" begin="12.85s"/>
       <audio src="desc2.rm" begin="33.71s"/>
       <audio src="desc3.rm" begin="42.65s"/>
       <audio src="desc4.rm" begin="59.80s"/>
     </priorityClass>
  </excl>
</body>

</smil>

Common Failures Identified by the Working Group

The following are common mistakes which are considered failures of this success criterion by the working group.

Optional Techniques (Advisory) for 1.2 L3 SC2

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.

Additional SMIL 1.0 Techniques (Advisory)

Provide audio descriptions in multiple languages by using the system-language attribute set to the language name of the language used in each extended audio description track.

Video with multi-language audio descriptions that pause the main media.

<body>

  <par>
   <seq>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="0s" clip-end="5.4" dur="8.7" fill="freeze"/>   
       <audio src="no1.wav" begin="5.4" system-language="de"/> <!-- only for german players -->
       <audio src="no1.wav" begin="5.4" system-language="en"/> <!-- only for english players, 
           there is no fallback in this config -->
     </par>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="5.4" clip-end="24.1" dur="20.3" fill="freeze"/>
       <switch>
	   <audio src="no2de.wav" begin="18.7" system-language="de"/> <!-- again, german -->
      	   <audio src="no2.wav" begin="18.7"/> <!--if not german, the switch moves to the next option, 
             which in this case has no test attribute, so it plays if the player language is set to !german -->
        </switch>
     </par>

     <par>
       <video src="video.rm" region="videoregion" clip-begin="77.4"/>
     </par>

   </seq>
  </par>
      
</body>

Additional SMIL 2.0 Techniques (Advisory)

Provide extended audio descriptions in multiple languages by providing audio tracks with the systemLanguage attribute set to the language name of the language used.

Video with multiple language extended audio description.

<smil xmlns="//www.w3.org/2001/SMIL20/Language">

<head>
   <layout>
     <root-layout backgroundColor="black" height="266" width="320"/>
     <region id="video" backgroundColor="black" top="26" left="0" height="144" width="320"/>
   </layout>
</head>

<body>	
   <excl>
     <priorityClass peers="pause">
       <video src="movie.rm" region="video" title="video"/>
       <switch>
         <audio src="desc1.rm" begin="12.85s"/>
         <audio src="desc1.rm" systemLanguage="de" begin="12.85s"/>
       </switch>
       <switch>
         <audio src="desc2.rm" begin="33.71s"/>
         <audio src="desc2.rm" systemLanguage="de" begin="33.71s"/>
       </switch>
       <switch>
         <audio src="desc3.rm" begin="42.65s"/>
         <audio src="desc3.rm" systemLanguage="de" begin="42.65s"/>
       </switch>
       <switch>
         <audio src="desc4.rm" begin="59.80s"/>
         <audio src="desc4.rm" systemLanguage="de" begin="59.80s"/>
       </switch>
     </priorityClass>
  </excl>
</body>

</smil>