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[media] Addressing "3.7 Requirements on the use of the viewport"

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Sat, 26 Jun 2010 11:48:21 +1000
Message-ID: <AANLkTil4fvfGD5jpmB7RoAYBCJecgnC6wvL9H-QGWWbk@mail.gmail.com>
To: Sean Hayes <Sean.Hayes@microsoft.com>
Cc: HTML Accessibility Task Force <public-html-a11y@w3.org>
Hi Sean,

(copied to list for documentation purposes)

This is the last section we are reviewing from the media requirements.
These are my initial thoughts.

Requirements on the use of the viewport

(VP-1) Text tracks don't have dimensions, they depend on the video
track. If there are text formats where this is not true, those formats
will not be used on the web. Remove this requirement.

Reply: UAAG 2.0 states the following:
"3.1.4 Rendering Alternative (Enhanced): Provide the user with the
global option to configure a cascade of types of alternatives to
render by default, in case a preferred type is unavailable. If the
alternative content has a different height or width, then the user
agent will reflow the viewport. (Level AA)"

Discussion: Text tracks may have dimensions, but they should be
provided relative to the video viewport rather than as absolute sizes
IMO. Alternative content could also be other videos, so this makes
reflowing the viewport still a requirement. It is, however, a question
whether reflowing the viewport is acceptable, in particular if the
dimensions of the media were fixed by the author. May need to discuss
this in the media a11y group.

(VP-3) Can this be made more specific? Is it about being able to scale
overlay sign language video tracks, or also about some other kind of

Reply: The intent of this criterium as per UAAG 2.0 is "User needs
video larger but still needs access to other application (take notes
during playback), fullscreen does not allow that. Content should
reflow as user adjusts playback viewport." It seems it is about
scaling the video by the user beyond its current size, but not to
fullscreen. This may also relate to sign language, but it seems not
the primary concern of UAAG.

Discussion: We should make it more specific and talk about the intent
of the criterium, e.g. the need for a resizing functionality on the
video viewport.

(VP-4) Is not currently possible since the <video> can be drawn on a
<canvas>, where the colors cannot be altered because of user
preference. No UA has such an option for images, why is it a
requirement for video? Suggest to remove this requirement.

Discussion: should discuss this with the larger media a11y group. I
also wonder if the need to change contrast and brightness is attached
at too low a level with the video and should just be done for the
whole screen, which is already possible through other means.

(VP-5) All browsers use this area for controls. What is the suggested

Reply: I think the idea of this requirements is to make sure to avoid
overlap of controls and captions, such that when controls are
displayed, the captions are moved up above them. Should discuss with
larger media a11y group if that was the intention.

(VP-3) Need details about how this is supposed to work, eg. does the
video pop up over the page content or does the rest of the page
reflow? Is page zoom enough? "with the ability to preserve aspect
ratio" - when would the user ever not want to preserve aspect ratio?

Reply: indeed - see 2. above

(VP-5) All existing browser, and many stand-alone media player
applications, place controls along the bottom edge of the movie. Where
should they go instead?

Reply: see 4. above

VP-5 may not be relevant in some case for example if the video contain
essential information in this area overlapping it with caption make it
impossible to see

Reply: Maybe the requirement can be reformulated to talk about
avoiding overlapping of displayed content on the video, but in
particular in the lower third where lots tends to happen. It could be
made more concrete such as if there are video controls, and overlay
ads, and captions, then the captions should move up the highest, the
overlay below that, and the controls should always stay at the bottom

Again UA guidelines need to be introduced as recommended practice in a
content spec.

Reply: Yes, agreed, this needs to become much more concrete.

“(VP-1) If alternative content has a different height or width to the
media content, then the user agent will reflow the viewport.” – this
does not seem to account for a scenario when the view-port has already
been maximized, but remains small due to device limitations.

Reply: agreed - should be included with 1. above

“(VP-4) Provide the user with the ability to control the contrast and
brightness of the content within the playback viewport.” - appears to
be a user-agent device requirement and should already be addressed in
the UAAG. This is also to me a clear candidate for “SHOULD” language
as it does not account for limitations of various devices

Reply: agreed, see 3 above


This one again has several issues that may need addressing by the
whole media subgroup.

Received on Saturday, 26 June 2010 01:49:13 UTC

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