Bit Prediction for Offline CABAC Rate Control
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Solution Overview
Problem
The offline context-adaptive binary arithmetic coding (CABAC) in video coding processes faces challenges in real-time rate control performance, particularly during scene changes, leading to buffer overflow and inaccurate bit rate control due to delayed reflection of input YUV value changes.
Innovation Solution
A bit prediction-based bit rate control method that determines an input bit count for a rate quantization model and updates the quantization parameter using predicted bit count information from the offline CABAC module, ensuring accurate buffer level calculation and minimizing errors by utilizing delay frame bit count information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If offline CABAC module is used to eliminate pipeline stalls, then encoding speed stability is improved, but rate control accuracy deteriorates due to frame delay
Solution Approach 1:
The patent applies preliminary action by using the offline CABAC module to pre-process and determine bit count information for future frames before actual encoding occurs. This allows the rate control module to have advance knowledge of expected bit consumption, enabling proactive QP adjustment rather than reactive adjustment after the fact. The offline processing of CABAC provides predictive bit count data that is used to set appropriate QP values in advance for maintaining accurate rate control.
Solution Approach 2:
The patent introduces an intermediary bit count information structure that bridges the offline CABAC module and the rate control module. This intermediary component processes and translates the offline CABAC output into usable bit count predictions for rate control decisions. It acts as a mediator that reconciles the timing mismatch between offline processing and real-time encoding requirements, allowing accurate rate control despite the frame delay inherent in offline CABAC operation.
2Productivity
If offline CABAC is used, then pipeline stall is eliminated, but buffer overflow occurs during scene changes due to delayed bit count reflection
Solution Approach 1:
The patent implements feedback by continuously monitoring actual bit count outcomes and using this information to refine future bit count predictions. The rate control module receives feedback from the encoding process about actual bit consumption patterns, and this feedback is used to adjust the QP settings dynamically. This closed-loop feedback mechanism allows the system to adapt to scene changes and varying content characteristics, preventing buffer overflow while maintaining the efficiency benefits of offline CABAC processing.
Solution Approach 2:
The patent applies dynamics by making the QP setting process adaptive and dynamic rather than static. The rate control module dynamically adjusts QP values based on real-time feedback about actual bit consumption versus predicted bit consumption. This dynamic adjustment capability allows the system to respond to changing scene characteristics, such as sudden increases in complexity during scene transitions, thereby maintaining reliable buffer level control while preserving pipeline efficiency through offline CABAC processing.
Data Source
AI summary
Provided is a bit rate control methods includes determining an input bit count for a rate quantization model according to a target bit rate setting; and providing a quantization parameter value determined through the rate quantization model to an encoder unit based on the input bit count. The rate quantization model is updated according to a prediction bit count information predicted from a BIN count information of a current or delay frame encoded in an encoder unit and the delay bit count information of the delay frame obtained from an offline context-adaptive binary arithmetic coding CABAC module.