Statistical Adaptive Video Rate Control Using Pixel Variance
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Solution Overview
Problem
Existing video rate control methods struggle to maintain optimal image quality and bit rate, often resulting in undesirable differences in image quality due to simplistic rate control mechanisms that fail to account for long-term image behavior, leading to anomalies such as varying quantization parameters across different parts of an image.
Innovation Solution
A method for determining a quantization parameter based on pixel variance and output bits over time, using a modified variance formula and adaptive quantization parameter calculation that considers both current and previous time periods, along with motion vector information, to maintain a stable bit rate and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple rate control mechanism is used to determine Qp, then the computational load is reduced, but image quality anomalies occur due to failure to account for long-term image behavior
Solution Approach 1:
The patent applies preliminary action by calculating and storing long-term average statistics (mean and variance) of image data before the actual encoding process. These pre-calculated statistics are then used to guide the rate control decisions, allowing the system to account for long-term image behavior without adding complexity during the real-time encoding process. This resolves the contradiction by preparing necessary information in advance.
Solution Approach 2:
The patent introduces an intermediary mechanism - a buffer that stores historical Qp values and image statistics over multiple frames. This buffer acts as a mediator between simple rate control calculations and the need for long-term image behavior awareness. By referencing this intermediary storage, the system achieves consistent image quality without requiring complex real-time analysis.
2Speed
If Qp is determined over a short period of time, then the rate control responds quickly to changes, but undesirable differences in image quality appear between different parts of the image
Solution Approach 1:
The patent merges short-term and long-term statistics by combining current frame image data with historical average statistics from previous frames. The Qp determination process integrates both immediate image characteristics and long-term trends, ensuring that rate control responds quickly to local variations while maintaining overall image quality consistency. This merging approach resolves the contradiction between response speed and quality uniformity.
3Productivity
If the degree of quantisation is frequently adjusted to match bit rate, then the bit rate constraint is met, but image quality fluctuates due to insufficient smoothing of image statistics
Solution Approach 1:
The patent applies beforehand cushioning by using a buffer to smooth out variations in image statistics before they affect quantisation decisions. The buffer accumulates image data over multiple frames, providing a cushioned, averaged view of image complexity. This prevents abrupt quantisation adjustments and stabilizes image quality while still meeting bit rate constraints through gradual, informed adjustments.
Solution Approach 2:
The patent implements feedback by continuously monitoring both current and historical image statistics, buffer fill levels, and Qp values. This multi-source feedback loop allows the rate control mechanism to make informed adjustments that balance bit rate compliance with image quality stability. The feedback from long-term statistics prevents over-reaction to temporary variations in image content.
Data Source
AI summary
A method and apparatus for video rate control for a video encoding system for encoding a video signal includes determining 12 a variance of pixel values over a time t of the video signal and calculating 13 a quantization parameter for the time t using the pixel variance and a number of output bits for the time t and a quantization parameter, pixel variance and a number of output bits used for an immediately previous time t−1.