Tweak understanding for 1.2.3 and 1.2.5

understanding/20/audio-description-or-media-alternative-prerecorded.html

@@ -20,9 +20,10 @@ <h2>Intent of Audio Description or Media Alternative (Prerecorded)</h2>
 
       <p>One approach is to provide audio description of the video content. The audio description
          augments the audio portion of the presentation with the information needed when the
-         video portion is not available. During existing pauses in dialogue, audio description
-         provides information about actions, characters, scene changes, and on-screen text
-         that  are important and are not described or spoken in the main sound track.
+         video portion is not available. Audio description provides information about actions,
+         characters, scene changes, and on-screen text that is important and not described
+         or spoken in the main sound track. Audio description is added during existing
+         pauses in the dialogue.
       </p>
 
       <p>The second approach involves providing all of the information in the synchronized
@@ -39,6 +40,10 @@ <h2>Intent of Audio Description or Media Alternative (Prerecorded)</h2>
          more complete representation of the synchronized media content than audio description
          alone.
       </p>
+
+      <p>If the original audio does not have sufficient pauses in the dialogue, authors need to provide
+         an appropriate alternative instead.
+      </p>
 
       <p>If there is any interaction as part of the synchronized media presentation (e.g.,
          "press now to answer the question") then the alternative for time-based media would

understanding/20/audio-description-prerecorded.html

@@ -16,12 +16,21 @@ <h2>Intent of Audio Description (Prerecorded)</h2>
       <p>The intent of this Success Criterion is to provide people who are blind or visually
          impaired access to the visual information in a synchronized media presentation. The
          audio description augments the audio portion of the presentation with the information
-         needed when the video portion is not available. During existing pauses in dialogue,
-         audio description provides information about actions, characters, scene changes, and
-         on-screen text that are important and are not described or spoken in the main sound
-         track.
+         needed when the video portion is not available. Audio description provides information about actions,
+         characters, scene changes, and on-screen text that are important and are not described
+         or spoken in the main sound track. Audio description is added during existing
+         pauses in the dialogue.
       </p>
 
+      <div class="note">
+         <p>This success criterion applies to all videos that contain "important visual details that cannot be understood from the main soundtrack alone". If the original audio
+            offers no pauses in the dialog where audio descriptions can be provided, then the content fails this success criterion -- no audio descriptions have been provided. However, the information can still be made available to users through other time-based media requirements at A and AAA levels.</p>
+            <p>Where all pauses in the dialogue contain audio descriptions, yet additional important visual information has not been described, the video can provide that additional content through either extended audio descriptions or a combination of A and AA. As noted in the [Time-based media guideline](https://www.w3.org/WAI/WCAG22/Understanding/time-based-media), "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."
+            favour of an audio description without losing important information. In these cases,
+            the content will fail this success criterion.
+         </p>
+      </div>
+
       <div class="note">
 
          <p>