Mpeg-4 Object Types, Profiles And Levels - MULTIMEDIA

Like MPEG - 2, MPEG - 4 defines many Profiles and Levels for various applications. The standardization of profiles and levels in MPEG - 4 serves two main purposes: ensuring inter ­ operability between implementations and allowing testing of conformance to the standard. MPEG - 4 not only specified Visual profiles and Audio profiles but also Graphics profiles, Scene description profiles, and one Object descriptor profile in its Systems part. We will briefly describe the Visual profiles in this section.

Since MPEG - 4 scenes often contain more than one video object, the concept of object type is introduced, to define the tools needed to create video objects and the ways they can be combined in a scene.

Table Tools for MPEG - 4 natural visual object types

Tools for MPEG - 4 natural visual object types

The above table shows the various tools applicable to the MPEG - 4 natural visual object types. For example, for object type "core", only five tools are used. Tools such as "gray - level shape coding", "sprite", "interlace", and so on, will not be used.

Table MPEG - 4 Natural Visual Object Types and Profiles

MPEG - 4 Natural Visual Object Types and Profiles

The above table shows these object types in MPEG - 4 visual profiles. Main profile, for example, supports only object types "simple", "core", "main", and "scalable still texture".

Table MPEG - 4 Levels in Simple, Core, and Main Visual Profiles

MPEG - 4 Levels in Simple, Core, and Main Visual Profiles

The above table lists the levels supported by the three most commonly used Visual profiles: simple, core, and main. For example, although CIF (352 x 288) is supported in four different levels (levels 2 and 3 in simple profile, level 2 in Core profile, and level 1 in Main profile), very different bitrates and maximum numbers of objects are specified. Hence, different qualities for CIF videos would be expected.


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