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Re: [me-media-timed-events] event is not defined (#41)

From: Chris Needham via GitHub <sysbot+gh@w3.org>
Date: Tue, 30 Apr 2019 13:53:26 +0000
To: public-web-and-tv@w3.org
Message-ID: <issue_comment.created-487961057-1556632404-sysbot+gh@w3.org>
Thanks @cconcolato, @ingararntzen for your valuable feedback.

> Cyril: This definition is based on the word event which is not defined. Is it an Event as defined in HTML? Or something else?

I agree, we have some ambiguity here. DASH `emsg` is one of the motivations behind this work, but by "event" we're mainly talking about the DOM events triggered at cue start and end times, which we expect to be synchronized to media playback.

> Cyril: Also the timing model for this event is not clear. Is an event instantaneous (i.e. specified by only one time in the media timeline) or long-running (with an end time on the media timeline)?

I don't think we have use cases in this document for instantaneous events, so happy to drop this, all the examples have both start and end times. More on this below...

> Ingar: For reference, in the implementation of the the sequencer for the timingobject I define cue as an object with properties (key, interval, data). The interval defines a region on the timeline (low, high). A point on the timeline is simply a special case of region, where both interval endpoints happen to be the same low == high.

I agree. You can create an instantaneous (point) event by making a `TextTrackCue` with times equal to each other. In practice, I've found that these generate `onenter` and `onexit` events as expected, but there seems to be a minimum non-zero duration needed for the cues to appear in the `activeCues` list inside a `oncuechange` handler, and this duration differs between implementations.

At this stage, the only change to the timing model that we are proposing is to make the event triggering more accurate; something allowed by HTML but not mandated (see "time marches on").

GitHub Notification of comment by chrisn
Please view or discuss this issue at https://github.com/w3c/me-media-timed-events/issues/41#issuecomment-487961057 using your GitHub account
Received on Tuesday, 30 April 2019 13:53:27 UTC

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