Two-Pass Rate Control for Video Coding Using Lagrangian Relaxation
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Solution Overview
Problem
Existing video coding technologies face challenges in efficiently managing bit allocation across frames to maintain consistent video quality and minimize distortion, particularly due to frame dependencies and abrupt quality changes.
Innovation Solution
A two-pass rate control technique that estimates rate-distortion characteristics in the first pass to select optimal quantization parameters for the second pass, minimizing distortion or quality fluctuation, using models that simplify frame dependencies and apply Lagrangian relaxation to reduce computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional rate control algorithms are used, then bit allocation is performed without considering frame dependencies, but this results in significant quality fluctuation and distortion
Solution Approach 1:
The patent applies preliminary action by performing a first coding pass to estimate rate-distortion characteristics before the actual coding process. This preliminary estimation allows the system to pre-calculate optimal quantization parameters, eliminating the need for complex real-time adjustments during coding and thereby reducing overall algorithmic complexity while improving quality consistency
Solution Approach 2:
The patent implements feedback by using the rate-distortion characteristics estimated from the first pass to guide quantization parameter selection in the second pass. This feedback mechanism allows the system to adapt to frame dependencies and minimize quality fluctuation, directly addressing the reliability issue without requiring overly complex control structures
2Productivity
If dynamic rate adjustment is implemented to respond to scene changes, then bit rate can be optimized, but this causes significant quality fluctuation during transitions
Solution Approach 1:
The system performs preliminary estimation of rate-distortion characteristics in the first pass, which allows it to pre-determine optimal bit allocation strategies. This preliminary action enables smooth quality transitions during scene changes by having pre-calculated parameters ready, avoiding abrupt quality fluctuations while maintaining bit rate efficiency
Solution Approach 2:
The patent applies dynamics by allowing quantization parameters to vary adaptively based on estimated rate-distortion characteristics. This dynamic adjustment, guided by the preliminary estimation, enables the system to respond to scene changes smoothly, maintaining both productivity and quality consistency without the abrupt transitions caused by static rate control
3Reliability
If complex models are used to account for frame dependencies, then quality consistency improves, but computational complexity increases significantly
Solution Approach 1:
The patent segments the coding process into two distinct passes: a first pass for estimating rate-distortion characteristics and a second pass for actual coding with optimized parameters. This segmentation allows the system to perform simple, low-energy operations in each pass rather than using complex models throughout, thereby maintaining quality consistency while reducing computational energy consumption
Solution Approach 2:
The patent uses a simple, disposable estimation model in the first pass that can be discarded after providing its rate-distortion characteristics. This approach replaces complex, energy-intensive continuous modeling with a simple one-time estimation process, achieving quality consistency without the ongoing computational burden of complex frame dependency models
Data Source
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AI summary
This disclosure describes rate control techniques that can improve video coding based on a "two-pass" approach. The first pass codes a video sequence using a first set of quantization parameters (QPs) for the purpose of estimating rate-distortion characteristics of the video sequence based on the statistics of the first pass. A second set of QPs can then be defined for a second coding pass. The estimated rate-distortion characteristics of the first pass are used to select QPs for the second pass in a manner that minimizes distortion of the frames of the video sequence.