Parallel Video Encoder Rate Control via Parallelism Scaling
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Solution Overview
Problem
In parallel encoding systems, controlling the Quantization Parameter (QP) to maintain a desired output bit rate is challenging due to instability caused by the large effective gain of multiple encoders operating independently, leading to oscillation and failure to converge to an optimal value.
Innovation Solution
Determining the Quantization Parameter based on a measure of parallelism (P) among the encoders, specifically using the equation QP = (GAIN/P) * ERROR, stabilizes the control loop and improves rate control by adjusting the effective gain, thereby reducing oscillation and ensuring convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple encoders operate independently in parallel to increase encoding throughput, then productivity is improved, but the rate control stability deteriorates due to large effective gain causing oscillation
Solution Approach 1:
The patent introduces an intermediary mechanism (centralized rate controller or coordination protocol) that mediates between multiple independent encoders and the overall bit rate constraint. This intermediary collects feedback from each encoder about its current operation state and adjusts their individual QP values accordingly, preventing the oscillation that would occur if each encoder operated completely independently with high gain.
Solution Approach 2:
The patent dynamically changes the QP parameter for each encoder based on the measure of parallelism P. By adjusting QP values in response to the current operating conditions and the number of parallel encoders, the system adapts the effective gain to maintain stability while maximizing throughput. The relationship QP = f(P) establishes a parameter transformation that scales the control response appropriately for the degree of parallelization.
2Speed
If the Quantization Parameter is adjusted aggressively to quickly reach the target bit rate, then the convergence speed is improved, but oscillation increases causing failure to converge to an optimal value
Solution Approach 1:
The patent makes the system dynamic by adjusting the effective gain based on the measure of parallelism P. Rather than using a fixed aggressive gain that causes oscillation, the gain is dynamically scaled according to the current parallel encoding configuration. This allows the system to converge quickly when appropriate while preventing oscillation when the parallelism level would otherwise cause instability.
Solution Approach 2:
The patent implements a feedback mechanism where the actual bit rate output from parallel encoders is monitored and used to adjust the QP values for subsequent encoding. The feedback loop incorporates the measure of parallelism P to scale the adjustment magnitude appropriately, ensuring that corrections move the system toward the target bit rate without overshooting and causing oscillation.
Data Source
AI summary
An example method to perform rate control in a parallel encoding system including a plurality of parallel encoders is disclosed. The method may comprise determining a quantization parameter for one of the plurality of parallel encoders based on a measure of parallelism of the plurality of parallel encoders. The method may further comprise providing the quantization parameter to the one of the plurality of parallel encoders to encode a chunk of a video sequence to generate an encoded chunk based on the quantization parameter.