Descriptors for AC-4 frame rate

The frame rate of AC-4 audio is signaled by either a DASH EssentialProperty descriptor or a SupplementalProperty descriptor with the schemeIdUri attribute set to tag:dolby.com,2017:dash:audio_frame_rate:2017.

An EssentialProperty descriptor must be used for Dolby AC-4 adaptation sets with high frame rates, if an adaptation set (audio or video) with a lower frame rate is available in the same period.

In all other cases, an EssentialProperty descriptor must not be used, but a SupplementalProperty descriptor might be used.