Rate Control in Video Coding

An encoder for coding a video sequence to generate a compressed bit stream, the encoder comprising:

• a rate control component configured to generate a quantization step size for quantizing coding blocks in the video sequence;
• and
• a quantizer component configured to quantize the coding blocks using the quantization step size,
• wherein the rate control component generates the quantization step size by
• computing a sequence base quantization step size for a sequence of pictures in the video sequence;
• computing a picture base quantization step size for a picture in the sequence of pictures based on the sequence base quantization step size, a type of the picture, and a level of the picture in a rate control hierarchy.

A machine readable medium storing instructions for rate control in coding of a video sequence to generate a compressed bit stream, wherein execution of the instructions by a processor in a video encoder causes the video encoder to perform the actions of:

• computing a sequence base quantization step size for a sequence of pictures in the video sequence;
• computing a picture base quantization step size for a picture in the sequence of pictures based on the sequence base quantization step size, a type of the picture, and a level of the picture in a rate control hierarchy;
• and
• coding the picture using the picture base quantization step size to generate a portion of the compressed bit stream.

The machine readable medium of claim 18, wherein coding the picture using a number of bits further comprises:

• estimating a number of bits needed to code the picture before coding a sequence of coding blocks in the picture;
• increasing a quantization step size for the sequence of coding blocks when the estimated number of bits is larger than the maximum number of bits;
• and
• decreasing the quantization step size for the sequence of coding blocks when the estimated number of bits is smaller than the minimum number of bits.