Feature detection for supported event types

[chrisn]

Question from @wolenetz at the TPAC 2020 meeting on DataCue: Does there need to be feature detection so that web applications can discover which types of UA-generated events are exposed via DataCue?

A suggestion is to add this to Media Capabilities.

[chrisn]

This breaks down into two further questions:

• How to detect capability for different means of carrying the event information, e.g, HLS playlist or media in-band DASH emsg events?
• How to detect support for different types of message, e.g., for DASH emsg events, what event message schemas are supported?

Is capability detection for the latter needed? If an implementation supports surfacing DASH emsg events, can we assume it will expose all such events, regardless of event schema?

[jpiesing]

Is capability detection for the latter needed? If an implementation supports surfacing DASH emsg events, can we assume it will expose all such events, regardless of event schema?

A native DASH player would not expose events that are targeted at the DASH player such as MPD reload events.

[chrisn]

I don't think there's a need for capability detection for that case, as an implementation that can handle one emsg schema could equally handle any schema. In the context of an MSE based player (as native DASH playback is currently not defined by any web specs), is there a need for an API to subscribe by scheme id/value?