Bit Rate Estimation for AVC Intra Inter Mode Decision
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Solution Overview
Problem
The complexity of rate distortion optimization in Advanced Video Coding (AVC) encoders is high due to the need for exhaustive mode combinations and entropy coding, increasing computational load and complexity.
Innovation Solution
A bit rate estimation method that predicts the number of entropy coded bits based on quantized transform coefficients, avoiding entropy coding during Intra and Inter mode decisions, using properties of context-based variable length coding (CAVLC) to estimate the bit rate of a 4×4 quantized residual block by estimating the rate of each symbol separately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If exhaustive mode combinations and entropy coding are used for rate distortion optimization, then coding quality is improved, but computational complexity increases
Solution Approach 1:
The patent pre-calculates and stores the bit rate for each possible coefficient combination in lookup tables before the actual encoding process. During rate distortion optimization, the encoder directly retrieves pre-computed bit rate values instead of performing exhaustive entropy coding calculations, significantly reducing computational complexity while maintaining accurate rate distortion assessment for quality optimization
Solution Approach 2:
The patent creates simplified models of the entropy coding process by pre-computing bit rate characteristics for different coefficient patterns. These models serve as copies that approximate the complex entropy coding behavior without requiring actual entropy decoding operations during mode decision, thereby reducing computational load while preserving the essential rate-distortion tradeoff information
2Measurement precision
If exhaustive mode combinations and entropy coding are used for rate distortion optimization, then accurate rate-distortion performance is achieved, but encoding time increases
Solution Approach 1:
The patent pre-calculates bit rate values for all possible coefficient combinations and stores them in lookup tables before encoding. During rate distortion optimization, the encoder directly retrieves these pre-computed values, avoiding time-consuming entropy coding operations while maintaining accurate rate-distortion measurement for comparing different mode combinations
Solution Approach 2:
The patent uses simplified bit rate estimation models that are computationally inexpensive to evaluate during mode decision. These lightweight models provide sufficient accuracy for comparing encoding modes without requiring the full complexity of actual entropy coding, enabling faster rate-distortion optimization with acceptable precision
Data Source
AI summary
To reduce the complexity of rate-distortion cost computation in AVC (MPEG4 Part2/H.264), a bit rate estimation method is used to avoid entropy coding during Intra and Inter mode decision. The bit rate estimation method predicts the number of entropy coded bits based on the quantized transform coefficients, thus avoiding the need to entropy code the quantized transform coefficients at each decision iteration.