[whatwg] Thoughts on video accessibility

Calogero Alex Baldacchino alex.baldacchino at email.it
Tue Dec 9 17:45:59 PST 2008

Silvia Pfeiffer ha scritto:
> On Wed, Dec 10, 2008 at 6:59 AM, Calogero Alex Baldacchino
> <alex.baldacchino at email.it> wrote:
>> Anyway, the use of subtitles in conjunction with screen readers might be
>> problematic: a deeper synchronization with the media might be needed in
>> order to have the text read just during voice pauses, to describe a mute
>> scene, or to entirely substitute the sound, if the text provides a
>> translation for the speech (I guess such would be untrivial to do without
>> putting one's hands inside the media).
> I cannot see a problem with conflicts between screen reading a web
> page and a video on the web page. A blind user would have turned off
> the use of captions by default in his/her browser, since they can hear
> very well what is going on, just not see it. As long as the video is
> not playing, it is only represented as a video (and maybe a alt text
> is read out). When the blind user clicks on the video, audio
> annotations will be read out by the screen reader in addition to the
> native sound. These would be placed into silence segments.

I was thinking on a possible lack of synchronism, with enabled 
annotations, between the screenreader reading them, and the actual 
duration of corresponding silence segments, maybe because of not enough 
brief sentences (e.g. as a consequence of a non well-groomed translation 
in a certain language) and/or a slow reading (depending on the language 
peculiarities, or the user settings, or both, and anyway out of control 
for any UA), resulting in a cross sound between the end part of a read 
out annotation and the beginning of the next non-silence segment, 
perhaps repeatedly during playback. Maybe this is a borderline case.

> In the case of a video with a non-native language sound track, it's a
> bit more complicated. The native sound would need to be turned off and
> the screenreader would need to read out the subtitles in the user's
> native language as well as the audio annotations in the breaks. This
> many not be easy to set up through preferences in the Web browser, but
> it should be possible for the user to manually select the right tracks
> and turn off the video sound.
> Regards,
> Silvia.
If the "base" language of the video, or the provided languages, were 
indicated somewhere, in the metadata or in the enclosing xml file, 
perhaps such a switch might be automated (perhaps the corresponding 
preference might be something like "read subtitles when the media does 
not support your language" maybe coupled with the option "don't read 
subtitles when the media supported language(s) can't be identified."). I 
was also thinking about 'implied' subtitles, such as those showed in a 
film when some characters speak in different language from the "base" 
language of the rest of the content; in such a case, if distinguishing 
'implied' subtitles were possible somehow, it might be nice to turn down 
(or off, as needed) the volume and let a voice engine to speak them 
aloud. I guess a UA with an embedded voice technology (such as Opera 
Voice, or FireVox), could do a good job and keep audio and video 
synchronized in most cases, but involving an external software (such as 
a screen reader) the scenario might change (usually a screenreader can't 
be fastened or slowed, and stopping it - when reading annotations - 
after having fed some text, if at all possible, might be untrivial -- 
again, I'm not enough inside this stuff, so I can just suppose some 
borderline scenarios). Anyway, your proposal is nice, and, once 
widespread, screen readers developers might choose to provide some kind 
of support for synchronism (if needed to improve accessibility of 
audio/video contents).

Regards, Alex
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