W3C home > Mailing lists > Public > w3c-wai-gl@w3.org > July to September 2001

Re: Caption synchronization tolerance

From: Larry Goldberg <Larry_Goldberg@wgbh.org>
Date: Tue, 28 Aug 2001 09:30:07 -0400
To: Geoffrey Freed <geoff_freed@wgbh.org>, Guidelines WG <w3c-wai-gl@w3.org>, Gregg Vanderheiden <gv@trace.wisc.edu>, <w3c-wai-gl-request@w3.org>
Message-ID: <B7B1143E.434E%Larry_Goldberg@wgbh.org>
And let me add that when a broadcast or cable program is captioned offline
(pre-produced, not live) caption tolerance is ususally specified as within
one frame of video (1/30 of a second). That is, the data path and hardware
should not delay the appearance of a caption for more than one frame after
the author intended it to appear.

But the author may in fact decide for any number of reasons how and when
they want the caption to appear.  geoff's right about "subjectivity" in
caption authoring.

- Larry

>> Live captioning is delayed for a number of reasons --
>> including allowing people to read and correct the captions before
>> transmission.   That delay is unavoidable today.   Yet that delay would
>> be unacceptable in a captioned movie.
> GF:
> Actually, real-time captions are delayed primarily because it takes a few
> seconds for the captions to be written phonetically by a human, translated by
> computer and then inserted into the broadcast signal.  But, yes,
> stenocaptioners can make corrections as they write.
>> Also, when doing training, you want the captions to lead any important
>> visual event.  That is, you don’t want the person reading the caption
>> when they should be looking at the screen to see something critical.
> GF:
> Perhaps, but this sort of decision is subjective and should be left to the
> author.  There is no industry-standard synchronization minimum or maximum used
> in captioning or audio description, and it would be impossible to specify a
> tolerance that could be universally applied even in the best of circumstances.
> The guidelines should simply say that captions and descriptions should be
> "closely synchronized" or "reasonably synchronized" (take your pick) and leave
> it at that.  
> When the time comes, I'd be happy to supply you with examples of captioned/AD
> multimedia for the techniques document, too.
> Geoff/NCAM
> On Monday, August 27, 2001, Gregg Vanderheiden <gv@trace.wisc.edu> wrote:
>>> Meeting minutes say:
>>>> #67WC ask Geoff Freed or someone at WBGH.
>>>> JW GV didn't want a number.
>>>> Action WC: Ask Geoff.
>> Geoff?  Larry?
>> Gregg
>> -- ------------------------------
>> Gregg C Vanderheiden Ph.D.
>> Professor - Human Factors
>> Dept of Ind. Engr. - U of Wis.
>> Director - Trace R & D Center
>> Gv@trace.wisc.edu <mailto:Gv@trace.wisc.edu>, <http://trace.wisc.edu/>
>> FAX 608/262-8848 
>> For a list of our listserves send “lists” to listproc@trace.wisc.edu
>> <mailto:listproc@trace.wisc.edu>

Larry Goldberg, Director
Media Access Group
WGBH Educational Foundation
125 Western Ave.
Boston, MA  02134
E-mail:  Larry_Goldberg@WGBH.org
Web:  access.wgbh.org

617-300-3722 (direct voice/FAX)
617-300-3400 (main NCAM)
617-300-2489 (TTY)
Received on Tuesday, 28 August 2001 09:30:44 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 16 January 2018 15:33:38 UTC