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Rate Control in Video Coding

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 sub-picture in a video sequence. Constrains on buffer size and network BW

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Rate Control in Video Coding

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  1. Rate Control in Video Coding

  2. 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 sub-picture in a video sequence • Constrains on buffer size and network BW • Encode video at a more nearly constant bit rate Open Loop Encoding (VBR) For a particular source frame When source complexity varies … Closed Loop Rate Control (CBR)

  3. H.264 Rate Control • Virtual Buffer Model • simulate the fullness of the real decoderbuffer • 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

  4. Distortion Measures • SSD: sum of squared differences • MSE: mean square error • PSNR: peak signal-to-noise ration • SAD: sum of absolute differences

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