The 3GPP Dynamic Adaptive Streaming over HTTP (3GP-DASH) specified in this specification provides streaming services over HTTP. 3GP-DASH is a set of profiles of ISO/IEC 23009-1 [43], also known as MPEG-DASH, with some extensions. For this it specifies XML and binary formats that enable delivering content from standard HTTP servers to an HTTP-Streaming client and enables caching content by standard HTTP caches. The specification for 3GP-DASH primarily defines two formats:

1. The Media Presentation Description (MPD) describes a Media Presentation, i.e. a bounded or unbounded presentation of media content. In particular, it defines formats to announce resource identifiers for Segments and to provide the context for these identified resources within a Media Presentation. For 3GP-DASH, the resource identifiers are exclusively HTTP-URLs possibly combined with a byte range.
2. The Segment formats specify the formats of the entity body of the HTTP response to an HTTP GET request or an HTTP partial GET request with the indicated byte range through HTTP/1.1 as defined in RFC 2616 to a resource identified in the MPD. Segments typically contain efficiently coded media data and metadata according to or aligned with common media formats.

The MPD provides sufficient information for a client to provide a streaming service to the user by accessing the Segments through the protocol specified in the scheme of the defined resources, in the context of this specification exclusively HTTP/1.1. Such a client is referred to as a 3GP-DASH client in the remainder of the present document. However, this specification does not provide a normative definition for such a client. An informative client model to illustrate the formats defined in this specification is provided in clause 7.2. An informative example client behaviour description is provided in Annex A of ISO/IEC 23009-1 [43]. Figure 7-1 shows an architecture in which the formats defined in this specification are typically used. Boxes with solid lines indicate devices that are mentioned in this specification as they host or process the formats defined in this specification whereas dashed boxes are conceptual or transparent. This specification deals with the definition of formats that are accessible on the interface to the 3GP-DASH client, indicated by the solid lines. Any other formats or interfaces are not in scope of this specification. In the considered deployment scenario, it is assumed that the 3GP-DASH client has access to an MPD. The MPD provides sufficient information for the 3GP-DASH client to provide a streaming service to the user by requesting Segments from an HTTP server and demultiplexing, decoding and rendering the included media streams.

The normative aspects of 3GP-DASH formats are defined by

• the profiles defined in clause 7.3.
• the DASH Media Presentation as defined in clause 8.
• the usage of the 3GPP file format for DASH as defined in clause 9.

The clauses mentioned above may refer to normative aspects in clause 10 on Quality-of-Experience, normative Annex B and Annex H as well as ISO/IEC 23009-1 [43].

The design of the formats defined in this specification is based on the informative client model as shown in Figure 7-2. The figure illustrates the logical components of a conceptual 3GP-DASH client model. In this figure the 3GP-DASH Access Engine receives the Media Presentation Description (MPD), constructs and issues requests and receives Segments or parts of Segments. In the context of this standard, the output of the DASH Access Engine consists of media in container formats according to the ISO/IEC 14496-12 ISO Base Media File Format [11] and specifically the 3GP file format [4]. In addition, timing information is provided that maps the internal timing of the media to the time line of the Media Presentation.