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Re: [me-media-timed-events] DataCue or a more specific API for DASH and emsg events

From: boblund via GitHub <sysbot+gh@w3.org>
Date: Fri, 15 Jun 2018 18:32:52 +0000
To: public-web-and-tv@w3.org
Message-ID: <issue_comment.created-397706956-1529087571-sysbot+gh@w3.org>
The JSON proposed by @silviapfeiffer captures the contents of emsg. Does this task force agree that it meets the requirement to expose emsgs to JavaScript?

Then there is the question of API requirements. Seems to me that any of: 1) TextTrackCue.text, 2) VTTCue.text,  3) DataCue.data and 4) a dedicated EmsgEventCue could be used to convey the emsg data. In HTML5, the creation of DataCue resulted from the decision to drop the .text attribute from TextTrackCue. Semantically, they seem the same to me; both are exposing opaque data intended for JavaScript that will not be processed by the browser. There was a discussion [1] about adding the .text attribute back to TextTrackCue, which would seem to obviate the need for DataCue, but I don't see it in either WC3 HTML5.2 or WHATWG.

VTTCue.text is attractive since it exists but I agree with @nigelmegitt  that exposing emsgs as WebVTT feels a little awkward.

EmsgEventCue (as a subclass of TextTrackCue) seems like the most straightforward API for JavaScript use. Plus, the sub-typing approach seems to be what the HTML authors have in mind.

A related question is what other Cue formats are under consideration, e.g. TTML? Should the task force consider the broader set of requirements and approaches?

[1] https://www.w3.org/html/wg/wiki/User:Spfeiffe/TextTrackChange



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