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[Proposal] Checkpoint 4.5: Clarification that direct access rapid access requirement

From: Ian B. Jacobs <ij@w3.org>
Date: Thu, 30 Aug 2001 18:13:40 -0400
Message-ID: <3B8EBA94.A9D6422C@w3.org>
To: w3c-wai-ua@w3.org
Hello,

Provision one of checkpoint 4.5 in the 31 July draft [1] reads:

<BLOCKQUOTE>
 1. Allow the user to stop, pause, resume, fast advance, and fast
 reverse rendered audio and animations (including video and
 animated images) that last three or more seconds at their
 default playback rate.
</BLOCKQUOTE> 

At today's teleconf [2], we discussed whether "fast advance" and
"fast reverse" implied that to get from time 1 to time 2 in a
presentation, the advance/reverse functionality had to scan every
intervening point (like a physical cassette tape).

Please consider the following proposal.

 _ Ian

[1] http://www.w3.org/WAI/UA/WD-UAAG10-20010731/
[2] http://lists.w3.org/Archives/Public/w3c-wai-ua/2001JulSep/0220

--------
Proposal
--------

 1) Rapid access to (time) moments in audio and animation
    content is the essential navigation requirement.

 2) Serial access (e.g., "Go from where I currently
   am back as long as I hold the reverse button down, in
   increments of ten seconds.") is a sufficient approach 
   to satisfying this requirement. Provisions 3. and 4. 
   are only relevant to serial access mode.

 3) Direct access (e.g., "Go directly to the 5-minute mark")
    is a sufficient approach to satisfying this requirement.

 4) The user agent SHOULD provide a combination of both
   of these functionalities for rapid access. 
 
 5) The checkpoint should say nothing about the granularity
    of serial or direct access.

The following proposal clarifies provisions 1, 3, and 4
accordingly. Provisions 2 and 5 remain unchanged.

<NEW>
  1. Allow the user to stop, pause, and resume audio and
  animations (including video and animated images) that last
  three or more seconds at their default playback rate. 

  X. Allow the user to navigate efficiently (forward and
  backward) within the same audio and animation content. The user
  agent may satisfy this requirement through sequential or direct
  access techniques. Sequential access techniques include, for
  example, rewind in various time increments, forward to the next
  audio track, etc. Direct access techniques include access to
  video track number 7, to the 10-minute mark, etc.

  Y. When serial techniques are used to satisfy the previous
  requirement, the user agent is not required to play back
  content during advance or rewind (though doing so may help
  orient the user). For example, the user agent is not required
  to play an animation at double speed during a continuous fast
  forward.  Similarly, the user agent is not required to play
  back synchronized content during advance or rewind (e.g., an
  audio track synchronized with a video track).

  Note: The user agent should allow efficient navigation of audio
  and animation content through a combination of serial and
  direct access techniques, such as direct access to a chosen
  audio track, then serial access within that track (e.g., slow
  forward at first, then faster as the user continues to press a
  button).
</NEW>

Comments:

 1) "Navigate efficiently" is an expression used in provision 1 of
    checkpoint 9.9: 

      "Allow the user to navigate efficiently to and among
       important structural elements in rendered content."

 2) Previous versions of this checkpoint did not specify 
    a granularity for fast advance/reverse (e.g., whether
    increments should be less than one second for precision
    video playback, one second, 5 seconds, etc.). This version
    of the checkpoint imposes no minimal granularity requirement.

 3) Neither the old nor the new version of the checkpoint
    requires playback of content during fast forward or rewind.


-- 
Ian Jacobs (ij@w3.org)   http://www.w3.org/People/Jacobs
Tel:                     +1 718 260-9447
Received on Thursday, 30 August 2001 18:15:42 GMT

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