Hierarchical Rate Control for Stable Video Quality
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Solution Overview
Problem
Existing rate control techniques in video coding, particularly those based on the H.263 test model near-term 5 (TMN5), are inadequate for GOP structures that include B-pictures and/or have hierarchical coding structures, leading to insufficient quality control and potential quality degradation, especially during scene changes.
Innovation Solution
Implementing rate control that determines and modulates the base quantization step size (Qs) at the sequence level rather than at the picture level, adapting Qs based on the type of initial picture and level in the rate control hierarchy, and adjusting minimum and maximum coded sizes to manage scene changes, using subGOPs to stabilize quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If rate control is implemented at the picture level, then bit rate management is simplified, but quality control becomes insufficient especially during scene changes
Solution Approach 1:
The patent segments the rate control process into multiple hierarchical levels: sequence level (controlling base Qs for entire GOP), picture level (adjusting Qs for individual frames), and block level (fine-tuning Qs for specific regions). This segmentation allows independent optimization at each level, enabling precise quality control during scene changes while maintaining manageable complexity through structured organization.
Solution Approach 2:
The patent implements dynamic rate control by continuously adjusting quantization step sizes (Qs) based on real-time buffer fullness, scene change detection, and hierarchical position. The base Qs is modulated dynamically at sequence level, and picture-level adjustments occur continuously, allowing the system to adapt to varying video complexity and maintain optimal quality without fixed parameters.
2Manufacturing precision
If quantization step size (Qs) is decreased to retain more detail, then image quality improves, but bit rate increases
Solution Approach 1:
The patent dynamically changes the quantization step size parameter (Qs) based on multiple factors including buffer fullness, scene change detection, and hierarchical level. At sequence level, base Qs is modulated to control overall bit rate; at picture level, adjustments refine quality based on local complexity. This parameter adaptation allows the system to optimize the quality-bit rate trade-off in real-time.
Solution Approach 2:
The patent applies different quality levels to different regions and hierarchical levels. Important regions (such as those with high motion activity or scene changes) receive higher quality treatment with lower Qs values, while less important regions use higher Qs values to reduce bit rate. The hierarchical structure enables local optimization at sequence, picture, and block levels.
3Stability of the object's composition
If base quantization step size (Qs) is modulated at sequence level, then quality stability during scene changes improves, but control granularity decreases
Solution Approach 1:
The patent segments control into three hierarchical levels: sequence level (coarse control of base Qs for entire GOP), picture level (medium control of Qs for individual frames), and block level (fine control of Qs for specific regions). This segmentation provides both stability at sequence level through base Qs modulation and fine-grained control at lower levels, resolving the granularity issue.
Solution Approach 2:
The patent implements multi-level dynamic control where base Qs is modulated dynamically at sequence level for stability, while picture-level and block-level adjustments provide continuous fine-grained control. The system dynamically adapts Qs at all levels based on real-time conditions, maintaining both stability and granularity simultaneously.
Data Source
AI summary
A method of rate control in coding of a video sequence to generate a compressed bit stream is provided that includes computing a sequence base quantization step size for a sequence of pictures in the video sequence, computing a picture base quantization step size for a picture in the sequence of pictures based on the sequence base quantization step size, a type of the picture, and a level of the picture in a rate control hierarchy, and coding the picture using the picture base quantization step size to generate a portion of the compressed bit stream.