[Bug 24860] When can user agents honor the user preferences for automatic text track selection

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24860

Silvia Pfeiffer <silviapfeiffer1@gmail.com> changed:

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--- Comment #1 from Silvia Pfeiffer <silviapfeiffer1@gmail.com> ---
(In reply to Jon Piesing (HbbTV) from comment #0)
> This issue is raised on behalf of HbbTV - see http://www.hbbtv.org, an
> organisation specifying the use of web technologies in television receivers.
> HbbTV is in the process of adding the HTML5 video element to its
> specification. The current HbbTV specification uses the <object> element for
> presenting video in an HTML page.
> 
> The current HTML5 specification defines two circumstances under which
> automatic track selection for text tracks happens.
> 
> 1) "When a media element is popped off the stack of open elements of an HTML
> parser or XML parser, the user agent must honor user preferences for
> automatic text track selection, populate the list of pending text tracks,
> and set the element's blocked-on-parser flag to false." and
> 
> 2) "When a text track corresponding to a track element is added to a media
> element's list of text tracks, the user agent must queue a task to run the
> following steps for the media element:" ... "Honor user preferences for
> automatic text track selection for this element."
> 
> This language can be interpreted as only permitting user agents to honor
> "the user preferences for automatic text track selection" in these two
> circumstances. It can also be interpreted as saying that, while it is
> required in these two circumstances, it could happen at other times as well.

It happens only where the spec explicitly tells it to happen. If there are
other times when it should happen and those other times are not explained in
the spec, then the spec needs updating.


> We have a use-case for user preferences to be honored at other times.
> Specifically, TV receivers normally come with a remote control that includes
> a subtitle button. The user can press this button at any time.

That is a different use case of the ones you list above. In HTML5, there are
"user preferences" and there is "user interaction". What you are describing
here is "user interaction". "User preferences" as described above typically map
to browser settings.

What you are asking for, therefore, is a reaction to a user interaction via a
control of some sort (in browsers its typically an overlay menu from the video
controls, for a TV it could be the remote control). That is covered in this
paragraph:

"When a text track corresponding to a track element experiences any of the
following circumstances, the user agent must start the track processing model
for that text track and its track element:

* The track element is created.
* The text track has its text track mode changed.
* The track element's parent element changes and the new parent is a media
element.
"

In particular, when toggling subtitles on/off, the browser will set the "text
track mode" of all subtitles tracks to "disabled" and thus in the "time marches
on" algorithm, all disabled tracks cues will not be shown.

Your use case is therefore already covered by the spec and no change is needed.

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Received on Sunday, 2 March 2014 03:14:42 UTC