Video Bit Rate Control via Iterative Quantization Adjustment
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Solution Overview
Problem
Existing video bit rate control algorithms, such as MPEG-2 TM5, fail to adequately manage frame complexity changes and decoder buffer conditions, leading to suboptimal bit allocation and potential buffer underflow, while struggling to maintain acceptable video quality within DVD performance constraints.
Innovation Solution
A method that iteratively adjusts nominal quantization parameters and masking strength parameters to control video bit rates, partitioning the video sequence into segments and recalculating quantization parameters based on visual activity to achieve a target bit rate while avoiding file oversizing, decoder buffer underflow, and GOP oversizing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MPEG-2 TM5 rate control algorithm is applied to video sequences, then device processing capacity and read rate constraints are met, but frame complexity changes due to scene changes are not handled well and bit allocation is not proportionate and timely
Solution Approach 1:
The patent implements a two-pass rate control algorithm that dynamically adjusts quantization parameters in response to scene changes. The first pass analyzes frame complexity and generates initial QP values, while the second pass refines these values based on actual bit consumption and scene change detection, enabling the system to adapt bit allocation dynamically to varying frame complexity while maintaining processing constraints
Solution Approach 2:
The patent performs preliminary analysis in the first pass by calculating frame complexity metrics and generating initial quantization parameter values before actual encoding. This preliminary action allows the system to prepare appropriate bit allocation strategies in advance, so when scene changes occur during encoding, the rate control algorithm can respond timely with pre-computed adjustments rather than reacting with delay
2Speed
If two-pass rate control algorithm is implemented to react rapidly to scene changes, then response time to scene changes improves, but initial learning period after each scene change occurs and buffer underflow may result
Solution Approach 1:
The patent implements feedback mechanisms in the second pass where the rate control algorithm monitors actual bit consumption against target bit rates and adjusts quantization parameters accordingly. The algorithm uses feedback from frame complexity analysis and previous encoding results to refine QP values, ensuring that bit allocation responds rapidly to scene changes while maintaining buffer levels through continuous adjustment based on actual encoding performance
Solution Approach 2:
The patent changes quantization parameter values dynamically based on detected scene changes and frame complexity metrics. When scene changes are detected, the algorithm adjusts QP values to allocate more bits to complex frames and fewer bits to simple frames, with the two-pass approach allowing these parameter changes to be computed and applied without causing buffer underflow
3Device complexity
If rate control algorithm does not adequately model decoder buffer conditions, then bit rate determination is simplified, but buffer underflow occurs
Solution Approach 1:
The patent performs preliminary buffer condition modeling in the first pass by analyzing frame complexity and estimating bit requirements. This preliminary buffer modeling allows the algorithm to plan bit allocation in advance, ensuring that enough bits are allocated to maintain buffer levels without requiring complex real-time buffer management during the actual encoding process
Data Source
AI summary
This invention is directed to a video bit rate control method for encoding a video sequence based on a decoder buffer condition and a group of picture (GOP) size limitation of the encoded video sequence. The method includes iteratively adjusting a quantization parameter and/or a masking strength parameter and encoding the video sequence at the adjusted parameters until the buffer condition and GOP size limitation are satisfied. The method makes the above adjustments to avoid buffer underflow and GOP oversizing.