H.264 Rate Control

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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
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