Selecting AdaptationSet dependent on language/accessibility preferences

[wschidol]

We propose to add functionality to have dash.js select the default audio AdaptationSet according to dash-if IOP v4.3, evaluating language/accessibility preferences. The feature is important for media delivery in open specification-based ecosystems and broadcasted content, e.g. ATSC-3 scenarios. HbbTV applications would also benefit from this functionality.

In these cases, one manifest file would be used to provide all the available combinations of language and accessibility (such as audio description), and dash.js be called upon to make the selection.

To keep backwards compatibility, this behavior would only be triggered if preferences are explicitly provided to dash.js.

This would mirror functionality already present on most deployed TV sets, and supply DASH-IF specification defined behavior.

The alternative is to leave the selection logic to be implemented in every application. This has the downside of getting incompatible behavior when matching languages or interpreting accessibility features.

[wschidol]

Similar functionality has been suggested to DASH-IF by ATSC and was also mentioned as part of the 2022 dash.js plan by @dsilhavy .

[dsilhavy]

@wschidol Can we close this with the changes applied in #4018?

[stschr]

@dsilhavy : Yes, can be closed