Rate Control Rate Control in Video Codingin Video Coding

Rate ControlRate 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

For a particular source frame

When source complexity varies …

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 MeasuresDistortion 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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