[ttml2] Create an `#audio-presentation` feature (#1068)

nigelmegitt has just created a new issue for https://github.com/w3c/ttml2:

== Create an `#audio-presentation` feature ==
The [`#presentation`](https://www.w3.org/TR/ttml1/#feature-presentation) feature designator requires support for region layout and presentation, and line layout, neither of which is relevant to a TTML2 presentation processor whose rendered output is only audio. 

This means that an audio-only profile of TTML2 would not necessarily support `#presentation` and therefore would not support the TTML2 Presentation Profile, the intent of which is to be a minimal profile for presentation. 

The consequence is it would be reasonable to define a kind of presentation processor profile that does not conform to the minimal presentation profile requirements, which sounds nonsensical.

I propose that we add a new feature designator that applies to audio presentation only, which does not include the constraints implied by visual text layout requirements. For completeness we also could consider creating a minimal TTML2 audio presentation processor profile. 

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/1068 using your GitHub account

Received on Friday, 5 April 2019 16:28:45 UTC