advertisement

Rate Control in Video Coding Rate Control A rate control algorithm dynamically adjusts encoder parameters to achieve a target bitrate. It allocates a budget of bits to each GOP, individual picture and/or subpicture in a video sequence For a particular source frame When source complexity varies … Constrains on buffer size and network BW Encode video at a more nearly constant bit rate Open Loop Encoding (VBR) Closed Loop Rate Control (CBR) H.264 Rate Control Virtual Buffer Model simulate the fullness of the real decoder buffer Basic unit: picture, slice, MB Complexity Estimation Rate-Quantization Model (for a picture) QP Initializer DemandedBitsPerPixel = DemandedBitrate / (FrameRate * height * width) ΔQP-Limiter typically limits changes in QP to no more than ± 2 units between pictures Distortion Measures SSD: sum of squared differences MSE: mean square error PSNR: peak signal-tonoise ration SAD: sum of absolute differences 7 8 9 10 11