Parallel Rate Control for Video Encoder with Look-Ahead Buffer Prediction
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Solution Overview
Problem
In video encoding, multi-processor designs face challenges in maintaining buffer fullness and bit rate control due to pipeline delays, leading to potential underflow or overflow issues, which disrupt the video stream quality and require accurate prediction of buffer fullness and bit allocation for efficient encoding.
Innovation Solution
A method for operating a multi-processor video encoder that calculates and predicts the fullness of a coded picture buffer at different times to determine target bit sizes and quantization parameters, allowing for accurate bit allocation and prevention of buffer underflow or overflow by estimating future buffer conditions based on past data and complexity measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-processor parallel processing is used to increase encoding speed, then productivity is improved, but device complexity increases and buffer control accuracy deteriorates due to pipeline delays
Solution Approach 1:
The video encoder is divided into multiple independent processors (first processor for I/P pictures, second processors for B pictures) that operate in parallel. Each processor handles specific picture types independently, allowing simultaneous encoding operations while maintaining manageable complexity through functional segmentation.
Solution Approach 2:
The system performs preliminary buffer fullness calculations and bit allocation decisions before actual encoding occurs. The master processor calculates target bit sizes and quantization parameters in advance based on pipeline delay predictions, allowing slave processors to encode without real-time buffer feedback while maintaining control accuracy.
2Productivity
If parallel processing with pipeline delay is implemented, then productivity is improved, but measurement precision of buffer fullness deteriorates due to timing mismatches
Solution Approach 1:
The master processor performs preliminary calculations of buffer fullness at future time points (after pipeline delay) before encoding begins. This advance calculation allows the system to account for the known pipeline delay and make accurate bit allocation decisions without requiring real-time buffer feedback during parallel encoding operations.
Solution Approach 2:
The system uses feedback from the virtual buffer model to continuously adjust bit allocation targets. The master processor monitors buffer fullness predictions and modifies quantization parameters and target bit sizes for subsequent pictures, creating a closed-loop control system that compensates for pipeline delays and maintains measurement precision.
3Reliability
If bit allocation is adjusted to maintain buffer fullness, then reliability is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The master processor combines multiple functions: it manages the virtual buffer model, calculates buffer fullness predictions, determines target bit sizes, and controls quantization parameters for all slave processors. This centralization of control functions improves reliability through coordinated buffer management while avoiding the complexity of distributed control mechanisms.
Solution Approach 2:
The rate control system uses the virtual buffer model as a self-regulating mechanism. The model automatically predicts buffer fullness and guides bit allocation decisions without requiring external intervention or complex real-time monitoring, allowing the system to maintain reliability through autonomous buffer management.
Data Source
AI summary
A method of operating a multi-processor video encoder by determining a target size corresponding to a preferred number of bits to be used when creating an encoded version of a picture in a group of sequential pictures making up a video sequence. The method includes the steps of calculating a first degree of fullness of a coded picture buffer at a first time, operating on the first degree of fullness to return an estimated second degree of fullness of the coded picture buffer at a second time, and operating on the second degree of fullness to return an initial target sized for the picture. The first time corresponds to the most recent time an accurate degree of fullness of the coded picture buffer can be calculated and the second time occurs after the first time.