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Re: ACTION-238 Revise guidelines 4.9.6

From: Markku Hakkinen <markku.hakkinen@gmail.com>
Date: Wed, 18 Nov 2009 14:58:00 -0500
Message-ID: <3dcaabaf0911181158q5c3cd468h2db2a9e6364203fd@mail.gmail.com>
To: Jan Richards <jan.richards@utoronto.ca>
Cc: UAWG list <w3c-wai-ua@w3.org>
Hi Jan,

Yes, they do need to be normalized (and then resolve precision, 33.3%,
if going with percentages).

I put this out as a first pass at redrafting 4.9.6 to address both
media slow down and speed up.  Discussion needed.

What I am lacking is empirical data to back the upper and lower limits
for both speech and visual, and I am a hesitant to cast these numbers
in stone (even when drawn from other standards, e.g., talking books)
without being able to point to specific data saying why these numbers
are optimal (de facto recommendations?).

There is empirical data suggesting that speed up and slow down have
benefit, but what I don't have is data saying what rates are ideal.

I'll add that the software algorithms for time scale modification used
by both Windows Media Player and Quicktime player currently support
the desired range (though the quality of the original encoding may
affect perceived quality at the high and low ends of the range).   The
question remains, what should that range really be?


On Wed, Nov 18, 2009 at 2:22 PM, Jan Richards <jan.richards@utoronto.ca> wrote:
> Hi Mark,
> I think we could be more consistent in the way these are stated. In one case
> we say "1/3 to 3 times" implying 33%-300% and in another we say at least one
> setting between 40% and 60% which implies a lowest setting of 60% would be
> ok.
> Cheers,
> Jan
> Markku Hakkinen wrote:
>> 4.9.6 Playback Rate Adjustment for Multimedia Content.
>> The user can adjust playback rate of prerecorded content containing
>> speech audio tracks such that all of the following are true (Level A):
>> -  The playback rate should be user adjustable between 1/3 and 3 times
>> real time of the recorded content.
>> -  Recorded speech, whose playback rate has been adjusted by the user,
>> should utilize pitch maintenance in order to avoid degradation of the
>> speech quality.
>> If only a visual track is present, provide at least one setting
>> between 40% and 60% of the original speed. (Level A)
>> When audio and video tracks are expected to be synchronized,
>> synchronization is maintained as long as they are played at 75% of the
>> original speed or higher. (Level A)
>> The UA should provide a function that resets the playback rate to
>> normal (1x) . (Level A)
> --
> Jan Richards, M.Sc.
> User Interface Design Lead
> Adaptive Technology Resource Centre (ATRC)
> Faculty of Information
> University of Toronto
>  Email: jan.richards@utoronto.ca
>  Web:   http://jan.atrc.utoronto.ca
>  Phone: 416-946-7060
>  Fax:   416-971-2896
Received on Wednesday, 18 November 2009 19:58:54 UTC

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