Zero duration DASH event messages

[chrisn]

Discussed 17/5/2021 minutes.

It is possible for a DASH event message to have zero duration. When mapped to a DataCue instance, the startTime and endTime would have the same value.

Handling zero-duration cues in JavaScript requires use of the TextTrackCue onenter and onexit events instead of the TextTrack oncuechange event.

For details, see Requirements for Media Timed Events.

Assigning onenter and onexit handlers must be done for each cue. Because there is no API to notify the web application when the UA instantiates a cue, there is no straightforward way attach these event handlers. Hence the proposed TextTrack addcue event.

The only way to use cuechange is to make sure that the cue duration is longer than successive executions of time marches on.