MPEG-21 Digital Item Streaming
MPEG doc#: N8828
Date: January 2007
This document provides an overview of MPEG-21 (ISO/IEC 21000) Digital Item Streaming.
MPEG-21 defines a multimedia framework to enable transparent and augmented use of multimedia resources across a wide range of networks and devices used by different communities. The fundamental unit of distribution and transaction within the MPEG-21 framework is the Digital Item which is a structured digital object with a standard representation, identification and metadata  .
Part 2 of MPEG-21 defines a Digital Item Declaration (DID) Model and Digital Item Declaration Language (DIDL) for declaring Digital Items  .
Digital Item Streaming (DIS) is part 18 of MPEG-21 and enables the incremental delivery of a Digital Item (DID, metadata, resources) in a piece-wise fashion and with temporal constraints in such a way a receiving User may incrementally consume the Digital Item.
DIS defines the Bitstream Binding Language (BBL) for this purpose.
2 Bitstream Binding Language overview
BBL defines syntax and semantics to describe instructions on how a Digital Item (comprising the DID, metadata, and resources) can be fragmented and mapped into one or more delivery channels such as MPEG-2 Transport Streams or the Real-time Transport Protocol.
BBL is general and flexible enough to describe instructions for streaming a Digital Item no matter what its content. It is agnostic to the format of the data it is able to process, as well as the type of delivery channels to which the data can be mapped.
BBL allows different parts of a Digital Item to be mapped to separate delivery channels.
BBL Instance documents provide the streaming instructions for a specific Digital Item, and contain references to the DID and its resources. BBL Bindings are generic instructions for fragmentation of a given type and its mapping to a given delivery channel. Bindings can be re-used by BBL Instances for processing specific instances of the given type to the given delivery channel.
BBL uses the Bitstream Syntax Description Language (BSDL) tool defined in part 7 of MPEG-21 REF _Ref156816325 \r \h  to process binary resources.
Figure \IF SEQ aaa \c 0>= 1 "SEQ aaa \c \* ALPHABETIC A." SEQ Figure 1 — The BBL document model
BBL provides an abstraction layer between a Digital Item and its mapping to a specific delivery channel enabling different bitstreams to be created from a single Digital Item. This enables
¾ different views/subsets of the DI,
¾ different renderings of the content, and
¾ different bitstream formats.
BBL hence facilitates in enabling transparent and augmented use of multimedia resources across a wide range of networks and devices used by different communities
 ISO/IEC, Information technology – Multimedia framework (MPEG-21) – Part 1: Vision, Technologies and Strategy, ISO/IEC TR 21000-1:2004, 1 November 2004.
 ISO/IEC JTC 1/SC 29/WG 11, MPEG-21 Overview, ISO/IEC JTC 1/SC 29/WG 11 N 5231, October 2002.
 ISO/IEC, Information technology – Multimedia framework (MPEG-21) – Part 2: Digital Item Declaration, Second edition, ISO/IEC 21000-2:2005, 1 October 2005.
 ISO/IEC JTC 1/SC 29/WG 11, Introducing MPEG-21 DID – an Overview, ISO/IEC JTC 1/SC 29/WG 11 N 7422, July 2005
 ISO/IEC, Information technology – Multimedia framework (MPEG-21) – Part 7: Digital Item Adaptation, ISO/IEC 21000-7:2004, 21 October 2004.