Method and apparatus for dual pass rate control video encoding

A method of dual-pass rate control video encoding, comprising the steps of:

• receiving uncompressed input video including a sequence of pictures with a video encoder, the input video including a plurality of contiguous sequences of pictures each referred to as a Group of Pictures (GOP) that, when coded, begin with an I-picture in display order and end with a last picture before a next I-picture, the GOP also including picture types encoded as P pictures, B pictures and B-reference pictures;
• performing a first encoding pass of the uncompressed video with the video encoder to detect scene changes, to assign macroblocks to a pre-determined number of activity classes, and to determine a complexity of each picture within the sequence of pictures, wherein macroblocks refer to rectangular arrays of luma samples and two corresponding blocks of chroma samples in the pictures, activity class refers to different defined classes of macroblocks based on luma values of the pictures of the input video, and complexity is a number of bits generated per picture and activity class;
• performing a second encoding pass for rate control of the uncompressed video with the video encoder at a delay relative to the first encoding pass wherein information from the first encoding pass concerning the scene changes, the activity classes, and the complexity are used for rate control determined in the second encoding pass for producing and outputting a bit stream of compressed video and wherein quantizer values for rate control are determined by the second encoding pass for each macroblock on a per picture type and activity class basis;
• and
• during the second encoding pass, encoding each macroblock determined to require a maximum quantizer value by the video encoder as a skip picture if encoding the macroblock with a maximum quantizer value would cause an overflow of the coded picture buffer (CPB) of the video encoder.

A dual-pass rate control video encoder, comprising:

• a first pass encoder module for receiving uncompressed input video including a sequence of pictures, the input video including a plurality of contiguous sequences of pictures each referred to as a Group of Pictures (GOP) that, when coded, begin with an I-picture in display order and end with a last picture before a next I-picture, the first pass encoder module detecting scene changes within the input video, assigning macroblocks to a pre-determined number of activity classes, and determining a complexity of each picture within the sequence of pictures, wherein macroblocks refer to rectangular arrays of luma samples and two corresponding blocks of chroma samples in the pictures, activity class refers to different defined classes of macroblocks based on luma values of the pictures of the input video, and complexity is a number of bits generated per picture and activity class;
• a delay unit for receiving the uncompressed input video;
• and
• a second pass encoder module for receiving the uncompressed input video via said delay unit, for obtaining information from the first pass encoder module concerning the scene changes, the activity classes, and the complexity used to determine rate control of the uncompressed video, and for producing and outputting a bit stream of compressed video;
• at least one of said first pass encoder module and said second pass encoder module adjusting the boundaries of at least some of the GOPs to be aligned with the scene changes.