Rate control and bit allocation for low bit rate video communication applications

摘要

A method and apparatus is described for encoding a sequence of video frames at a target bit rate. A controller controls the bit r ate by providing values for a coding frame rate and quantization parameter to a frame encoder. A set of operating regions, including a first operating region and a second operating region, is defined. Each operating region includes a range of values for each parameter. These operating regions may intersect each other or be disjoint. The encoder codes the frame sequence with the value of each parameter being in the first operating region. During the coding, the controller determines to make an adjustment to the value of one parameter that would put that value out of the first operating region and in the second operating region. The controller makes the adjustment if a predetermined criterion is satisfied, otherwise the controller constrains the value of that one parameter to remain in the first operating region. In one embodiment, the criterion is that the value of that one parameter and the value of another parameter would be in the same operating region if the adjustment were made. In another embodiment, the criterion is that, when it is determined to make the adjustment to the one parameter, the value of another one of the parameters is in a predetermined region of the first operating region.