The visual profiles determine which visual object types can be present in the scene. This is also the way they are defined: as a list of admissible object types. Quite a few of them correspond to the most complicated object that they support, and they also have similar names. Below we will list the profiles and mention some application areas. Note again that these are only suggestions and that profiles were not designed for specific applications. This is also why their names are generic and refer to tools rather than applications or services.
- The Simple Profile only accepts objects of type Simple, and was created with low complexity applications in mind. The first usage is mobile use of (audio)visual services, and the second is putting very low complexity video on the Internet. Also small camera devices recording moving video to, e.g., disk or memory chips, can make good use of this profile. It supports up to four objects in the scene with, at the lowest level, a maximum total surface of a QCIF picture. There are 3 levels for the Simple Profile with bitrates from 64 to 384 kbit/s..
The levels also define the maximum total surface for the objects and the amount of macroblocks per second that the decoder needs to be able to decode. Further, they define the size of various (hypothetical) buffers needed for decoding. While the maximum total object size is defined, the aspect ratio is not prescribed. This gives maximum creative freedom. It could be used for instance in a personal computer screen, where a very wide or a very tall object could be created, or several smaller objects in various places on the screen, not confined to a typical QCIF area.
The same level philosophy is followed for restricting the complexity of the natural video objects in all the visual profiles. - The Simple Scalable Profile can supply scalable coding in the same operational environments as foreseen for Simple, and has 2 levels defined.
- The Core Profile accepts Core and Simple object types. It is useful for higher quality interactive services, combining good quality with limited complexity and supporting arbitrary shape objects. Also mobile broadcast services could be supported by this profile. The maximum bitrate is 384 kbit in Level 1 and 2 Mbit/s Level 2. While the levels do not prescribe the visual session size, they are created with a certain session size in mind, called the ‘typical visual session size’. For Simple this was QCIF, for Core it is QCIF and CIF for the two levels respectively. The amount of macroblocks is chosen such that a scene using this typical session size can have overlapping objects and still be ‘filled’.
- The Main Profile was created with broadcast services in mind, addressing progressive as well as interlaced material. It combines the highest quality with the versatility of arbitrarily shaped object using grey-scale coding. The highest level accepts up to 32 objects (of Simple, Core, or Main type) for a maximum total bitrate of 38 Mbit/s.
- The N-bit profile is useful for areas that use thermal imagers, such as surveillance applications. Also medical applications may want to use the enhanced pixel depth giving a larger dynamic range in colour and luminance. It accepts objects of type Simple, Core, and N-bit. Currently only one level is defined.
- The Scaleable Texture Profile is meant for audiographic applications. It was requested by companies that want to build mobile devices, which combine sound with synchronously displayed pictures, and possibly BIFS-based graphics, in very simple terminals.
- The Simple Face Profile accepts only objects of type Simple Face. Depending on the level, either one or a maximum of 4 faces can appear in the scene, e.g., for a virtual meeting. Bitrates remain very low; even for the second level, 32 kbit/s is more than adequate for driving a maximum of four faces.
- The Hybrid Profile allows combining both natural and synthetic objects in the same scene while keeping complexity reasonable. On the natural side, it compares to the Core Profile, while on the synthetic side, it adds animated meshes, scalable textures, and animated faces — a rich set of tools for creating attractive hybrid natural and synthetic content. This profile can be used to place ‘real’ objects into a synthetic world and also to do the opposite, adding synthetic objects to a natural environment
- The Basic Animated Texture Profile allows animation of still pictures and facial animation. Attractive content can be created at very low bitrates.
A partial hierarchy exists in the visual profiles, the same hierarchy that we described above for the corresponding object types. This means that Main is a superset of Core, which in itself is a superset of Simple. N-bit is a superset of Core. Simple Scalable is a superset of Simple, in such a way that the Simple profile can decode the base layer of Simple Scalable bitstream.
Work in MPEG is ongoing for amendments (additions) to the standard, beyond Version 2. MPEG has started research on MPEG-4 for Studio applications, notably in the visual area, which requires considerably higher bitrates than are currently supported. If this work is indeed continued (and there is every reason to believe that it will) then several new (visual) profiles are anticipated. Another research item probably leading to one or more new visual profiles is visual fine-grain scalability, a much desired feature already present in MPEG-4 audio.