Support for Initialization Set

[dsilhavy]

Description

From ISO/IEC 23009-1 Section 5.3.12.1

An Initialization Set provides a common set of media properties across Periods in a Media Presentation. If an Initialization Set with certain properties is provided in an MPD, there shall be at least one Adaptation Set in at least one Period with these properties. More importantly, it can also be indicated that all Periods in the Media Presentations include at least one Adaptation Set that follows the properties of the Initialization Set. Especially in the latter case. an Initialization Set can be selected at the start of a Media Presentation in order to establish the relevant decryption, decoding and rendering environment. This provides expected consistent playback behaviour for the DASH Client if it selects only Adaptation Sets that are included in the selected Initialization Set.