According to TS 26.501
, Downlink Media Streaming provides the ability for content to be distributed using procedures and protocols defined by 5G Media Streaming as shown in Figure 4.1-1. The detailed procedures for the interfaces and APIs for 5G Media Streaming are defined in TS 26.512
The present specification primarily deals with the segment formats delivered on M4d and the requirements applicable to the media playback platform and content decryption module. According to Figure 4.1-1, the Access Client in the 5GMSd Client uses the manifest, typically the MPD for Dynamic Streaming over HTTP (DASH) as defined in ISO/IEC 23009-1  and TS 26.247
or the Master Playlist for HTTP Live Streaming (HLS) as defined in RFC 8216
to download Segments to initiate a media playback session. A 5GMS Application Provider may define and ingest these segment formats directly through M2d such that the 5GMSd AS acts as a hosting server but does not require the media to be either transcoded or repackaged. Using these unified formats maximizes cacheability and general CDN operations, including usage of secure transport protocols such as HTTPS on M4d.
5G Media Streaming segment formats are defined based on the Common Media Application Format (CMAF) in ISO/IEC 23000-19 . By using this format, 5G Media Streaming is compatible with a broad set of segment-based streaming protocols including Dynamic Streaming over HTTP (DASH) and HTTP Live Streaming (HLS). For example, ISO/IEC 23009-1  defines a detailed DASH profile for delivering CMAF content within a DASH Media Presentation using a converged format for segmented media content.
Readers of the present document are encouraged to familiarize themselves with terms defined in CMAF such as CMAF Headers, CMAF Fragments, CMAF Tracks and CMAF Switching Sets. CMAF defines a content model for adaptive playback of segmented media (enabling seamless switching across tracks encoded from the same media) and late binding of tracks from different media types, associated with the same presentation. CMAF also defines a content protection and encryption framework for multi-DRM support based on ISO/IEC 23001-7 . Furthermore, CMAF defines media profiles, i.e. encoding constraints on a CMAF track and its contained media samples associated with a specific codec. This specification only uses the structural constraints of CMAF as defined in clause 7 of ISO/IEC 23000-19  and in clause 8 of ISO/IEC 23000-19  for encrypted content. Specific 5GMS media profiles for video, audio and subtitles based on the general constraints of ISO/IEC 23000-19  in clauses 9, 10 and 11, respectively, are defined in this specification. However, Downlink Media Streaming is not restricted to the media profiles defined in this specification: any CMAF media profile may be used and distributed within Downlink Media Streaming.