Last update: 2011/08/21
An overview of the other parts of the MPEG-4 standard.
Part 4 is Conformance and part 5, called Reference Software, u nlike MPEG-1 and -2 is not a Technical report (TR) with an informational value, but an International Standard (see here for more about this). Part 6 “Delivery Multimedia Integration Framework” (DMIF) provides a standard interface to access various transport mechanisms as described before. MPEG-4 also includes Part 7 “Optimised software for MPEG-4 tools” providing examples of reference software that not just implements the standard correctly but also in optimised form. Part 8 “4 on IP framework” complements the generic MPEG-4 RTP payload defined by IETF as RFC 3640 [8]. Part 9 “Reference Hardware Description” where the reference software is in Very-High-Speed Integrated Circuit (VHSIC) Hardware Description Language (VHDL) to synthesise VLSI chips.
MPEG 1 and MPEG-2 assume that information in decoded form leaves the decoder as sequences of PCM samples but the standards are silent on what is done with them. As described before MPEG-4 Scene Description (part 11), originally bundled with Part 1, provides technologies for the new functionality of “composing” different information elements in a “scene”.
The original technology is called Binary Format for MPEG-4 Scenes (BIFS) of which there exists a Java powered version called MPEG-J. A newer technology with similar functionalities, but restricted to 2D scenes, is provided by Part 20 “Lightweight Application Scene Representation” (LASeR).
MPEG-4 provides standard solutions for coding of synthetic visual information for 3D graphics. These tools are specified in Part 2 - Face and Body Animation and 3D Mesh Compression, Part 11 - Interpolator Compression - and 16 - a complete framework, called Animation Framework eXtension (AFX), for efficiently coding the shape, texture and animation of interactive synthetic 3D objects. AFX is an attempt at unifying MPEG-4’s tools related to 3D graphics.
An important component of AFX is 3D Mesh Coding to provide efficient encoding of 3-D polygonal meshes with
AFX introduces as well an advanced animation model for articulated models, a hierarchical representation of urban environments and several modern coding tools for 3D data.
Part 25 “3D Graphics Compression Model” specifies an architectural model able to accommodate third-party eXtensible Markup Language (XML) based description of scene graphs and graphics primitives with (potential) binarisation tools and with MPEG-4 3D Graphics Compression tools.
Synthetic Audio, called “Structured Audio”, is included in part 3. It provides the means to code sound using structured descriptions that are interpreted by a Structured Audio decoder to perform music and sound-effect synthesis. The Structured Audio Tools are: Structured Audio Orchestra Language (SAOL) providing synthesis methods, Structured Audio Score Language (SASL/MIDI) providing control parameters and Structured Audio Sample Bank Format (SASBF) providing the actual sample data.
The ISO Base Media File Format (part 12 of MPEG-4) is designed to contain timed media information for a presentation in a flexible, extensible format that facilitates interchange, management, editing, and presentation of the media. These may be ‘local’ to the system containing the presentation, or may be via a network or other stream delivery mechanism. Part 14 “MP4 File Format” extends the File Format to cover the needs of MPEG-4 scenes while part 15 “AVC File Format” supports the storage of AVC and MVC bitstreams.
The Streaming Text Format (part 17 of MPEG-4) defines text streams that are capable of carrying Third Generation Partnership Program (3GPP) Timed Text (specified in 3GPP TS 26.245). To transport the text streams, a flexible framing structure is specified that can be adapted to the various transport layers, such as RTP/UDP/IP and MPEG-2 Transport and Program Stream, for use in media such as broadcast and optical discs.
Among the remaining MPEG-4 technologies the Open Font Format (part 22) is worth mentioning. Thus is the result of the action taken by MPEG when it received a request from rights holders to convert the widely adopted OpenType specification to an ISO standard. As is the rule with MPEG standards, the OpenType specification was converted to a Working Draft and then balloted through the ISO-specified process of Committee Draft (CD), Final Committee Draft (FCD) and Final Draft International Standard (FDIS) stages.
The figure below provides a conceptual diagram of the structure of an MPEG-4 decoder with the role played by the main MPEG-4 technologies.
Figure 3 – MPEG-4 reference diagram
With reference to the figure the parts of the MPEG-4 standard specify the blocks as follows:
