Visual Media Coding and Transmission

5.2 Overview of the State of the Art

5.2.1 Rate Control

The rate control mechanism is one of the video coding tools not normatively specified in any of the currently available and emerging video coding standards, since this is not necessary for interoperability. However, rate control is related to one of the main degrees of freedom for improving the performance of standard-based systems. Generically, the major objectives of video coding rate control, whatever the coding architecture, can be summarized as:

• Regulation of the video encoder output data rate according to specific constraints.
• Maximization of the subjective impact of the decoded video.

In frame-based coding architectures, the rate control mechanism has, usually, the necessary degree of freedom to choose the best tradeoff in terms of spatial and temporal resolution, as well as to introduce (controlled) distortion in the texture data in order to maximize the global subjective quality of the decoded video, given the resources and conditions at hand.

In object-based coding architectures, the degree of freedom of frame-based video coding rate control appears for each object in the video scene. Additionally, there is the shape data, which defines the shape of each object, and the scene description data, which specifies which objects are in the scene and how the scene is organized. The major novelty here is the semantic dimension of the data model and consequently of the rate control mechanism. This mechanism can decide to ...