Video Encoder Rate Control via Adaptive Quantizer and Coefficient Dropping
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Solution Overview
Problem
Existing video encoding methods are inefficient and resource-intensive, particularly in achieving a specified encoded picture size, due to unpredictable file size and quality variations caused by quantizer changes, and are unsuitable for real-time applications.
Innovation Solution
A method that encodes a picture in a limited number of passes by using a universal quantizer initially, then adjusting to a second universal quantizer if necessary, and further to a local quantizer for slices exceeding size limits, ensuring the encoded picture size does not exceed a predetermined limit by dropping high-frequency coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a trial and error approach with multiple encoding passes is used to achieve a specified picture size, then the encoded picture size accuracy is improved, but the encoding time and computational resources increase significantly
Solution Approach 1:
The patent performs a first pass encoding to collect statistics about the picture data before final encoding. This preliminary analysis of the input data characteristics allows the system to predict the appropriate quantizer value in advance, avoiding multiple trial-and-error passes and significantly reducing encoding time while maintaining size accuracy.
Solution Approach 2:
The system uses feedback from the first pass encoding statistics to dynamically adjust the quantizer selection. By analyzing the actual picture content and bit consumption patterns from the preliminary pass, the system can make informed decisions about the optimal quantizer value, ensuring the encoded picture meets size requirements without excessive re-encoding.
2Productivity
If the quantizer is increased to reduce file size, then the compression ratio is improved, but the perceived picture quality deteriorates
Solution Approach 1:
The patent dynamically adjusts the quantizer parameter based on actual picture content characteristics rather than using a fixed or predetermined value. By changing the quantizer parameter adaptively according to the specific statistical properties of each picture, the system achieves optimal compression ratios while maintaining acceptable quality levels for different types of content.
3Manufacturing precision
If sequential processing of macroblocks is used to adjust quantizer dynamically, then the encoded picture size control is improved, but the device complexity and difficulty of parallel processing increase
Solution Approach 1:
The patent divides the encoding process into two distinct passes: a first pass for statistical analysis and quantizer determination, and a second pass for final encoding. This segmentation allows the complex task of dynamic quantizer adjustment to be separated from the main encoding loop, enabling parallel processing of multiple macroblocks in the second pass while maintaining size control through the preliminary statistics gathered in the first pass.
4Manufacturing precision
If multiple different quantizers are used across macroblocks to control picture size, then the encoded picture size accuracy is improved, but the visual quality variance between macroblocks increases
Solution Approach 1:
The patent determines a single universal quantizer value that applies to all macroblocks in the picture, rather than using different quantizers for different regions. This universal quantizer is selected based on comprehensive statistics from the first pass encoding, ensuring consistent visual quality across the entire picture while still achieving accurate size control through the adaptive selection process.
Data Source
AI summary
A method and system are provided for encoding a picture. The method includes encoding the picture into a first encoded picture using a first universal quantizer. If a size of the first encoded picture is greater than a maximum picture size, the method includes encoding the picture into a second encoded picture using a second universal quantizer. Before a second-pass encoding, the target size and maximum size for each slice is determined. During the second pass encoding, if a size of the encoded slice is greater than the maximum slice size, the method includes encoding the slice using a third local quantizer. If a size of the encoded slice is still greater than a maximum slice size, the method includes dropping coefficients from the encoded slice to ensure that the encoded size never exceeds the maximum size.