Efficient coding complexity estimation for video transcoding systems

摘要

Systems and methods of transcoding video bitstreams that employ highly efficient look-ahead approaches to video transcoding. The systems and methods perform video transcoding in the pixel domain to make successive adjustments to estimates of the coding complexity of video frames in input video bitstreams. The systems and methods can employ the adjusted estimates of the coding complexity in a rate control function to provide improved bit allocations for the video frames in transcoded output video bitstreams, thereby enhancing overall perceptual quality.

主权项

1. A method of transcoding a video bitstream in a video transcoding system, the video transcoding system including a video bitstream analyzer, a video decoder, and a video encoder, the method comprising the steps of:
receiving, at the video bitstream analyzer, an input video bitstream including a plurality of video frames from an input video sequence, the respective video frames being encoded in a first coding format; for each of at least some of the plurality of video frames in the input video bitstream:
generating, by the video bitstream analyzer, an estimation representing a coding complexity of the respective video frame; andadjusting, by the video bitstream analyzer, the estimation representing the coding complexity of the respective video frame, the adjusting including:
obtaining one or more of (1) a first adjustment parameter that is a first function of a current quantization parameter (QP) used to encode the respective video frame, (2) a second adjustment parameter that is a second function of a temporal distance between the respective video frame and a reference video frame used to encode the respective video frame, and, (3) in the event the respective video frame is encoded in the first coding format as a P-frame, a third adjustment parameter that is a third function of a difference between a reference QP used to encode the reference video frame and the current QP;applying one or more of the first, second, and third adjustment parameters to the estimation representing the coding complexity of the respective video frame to obtain an adjusted coding complexity estimation of the respective video frame; andin the event the respective video frame is encoded in the first coding format as the P-frame, applying, at least at some times, a fourth function to the adjusted coding complexity estimation of the respective video frame, the fourth function being expressed as,
CF(current_frame)=ω1*CF(previous_frame)+ω2*CF(current_frame)+ω3*CF(next_frame),wherein “CF(current_frame)” is the adjusted coding complexity estimation of the respective video frame, “CF(previous_frame)” is a predetermined coding complexity of a previous P-frame in the input video bitstream, “CF(next_frame)” is another predetermined coding complexity of a next P-frame in the input video bitstream, and “ω1”, “ω2”, and “ω3” are each a predetermined weighting value; decoding, by the video decoder, the plurality of video frames to generate a plurality of decoded video frames; and encoding, by the video encoder, the plurality of decoded video frames in a second coding format to generate a plurality of transcoded video frames in an output video bitstream, the encoding including applying a rate control function to at least some adjusted coding complexity estimations of the respective video frames to determine bit allocations for the plurality of transcoded video frames in the output video bitstream.