[Bug 24416] New: Ambiguous support for native in-band captioning.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24416

            Bug ID: 24416
           Summary: Ambiguous support for native in-band captioning.
           Product: HTML WG
           Version: unspecified
          Hardware: Other
                OS: other
            Status: NEW
          Severity: major
          Priority: P2
         Component: HTML5 spec
          Assignee: dave.null@w3.org
          Reporter: graham.clift@am.sony.com
        QA Contact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-admin@w3.org,
                    public-html-wg-issue-tracking@w3.org

Sometimes native captioning is supported by a decoder for regulatory reasons
and cannot always physically be made available to the user agent and/or
application. In addition native inband captions like CEA-708 are often highly
optimized and converting these to a User Agent format like WebVTT can cause
performance and captioner intent loss. Also, important cue information like
endtime might only be available with the start of the next caption and trick
play operation or continuous live streaming can corrupt cue timing accuracy
compared to native captioning. 

The application or user agent would therefore benefit from making use of
optimized native captioning. The controls feature offers one way to do this at
the user agent level however from JS only the TextTrack mode='showing' is
provided. Yet, setting mode='showing' has other meanings, i.e. the captions
that are stored in cues are being displayed, some of which may already have
been created or modified out-of-band. In addition no knowledge of the native
capability of the platform is being registered to the application in order to
change this behavior. 

We need a way for the user agent to convey to JS support for native captions
and for the application to have a method to turn them on or off. 

Also, if the native cues can be passed to application level in 'hidden' mode
how can we convey that timing accuracy is not guaranteed but the data can be
used by the application for other non-critical timing sensitive uses (like
caption content search)? In this case, what type of 'hidden' TextTrackCue would
we use..dataCue?

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Received on Monday, 27 January 2014 23:40:00 UTC