Support for 'emsg' boxes when playing HLS manifest with CMAF segments

[duggaraju]

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Additional context

For DASH the list of supported 'emsg' schemas specified in the DASH manifest. Any emsg box that belongs to a schema not in the list is ignored by the player. For HLS there is no such equivalent in the manifest. (Except for ID3).

If we can expose emsgSchemedIdUris as an optional array of schemes on shaka.extern.HlsManifestConfiguration that the user can set then the emsg events can be fired during HLS playback as well.

[joeyparrish]

Alternately, we could have a boolean config that enables watching for and dispatching all emsg boxes, regardless of schema. Would that be easier to configure or more useful, or would you prefer to limit it to a list of known, expected schemas?

[duggaraju]

A boolean config could work too. But it would need some plumbing since the check for the schema is done in streaming_engine.js while the filling of the emseSchmeIdUris is done under manifest parser. You would need some special value (instead of default null) to indicate all schemas.

[duggaraju]

Thanks. You can close the issue.