Hybrid Bitrate Constrained Audio Encoding
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Solution Overview
Problem
Current audio coding techniques, such as VBR codecs, often result in bitrates that are either too high, wasting bits, or too low, leading to undesirable sound quality due to inaccuracies in psychoacoustic models and masking thresholds, which fail to perfectly match human perception of sound quality.
Innovation Solution
A hybrid bitrate constrained variable bitrate coding approach that incorporates both Average Bit Rate (ABR) and Constant Bit Rate (CBR) encoding modes, with a secondary quantization loop to adaptively control the final bitrate for each audio block, ensuring it falls within a specified range to meet sound quality targets, thereby optimizing bitrate usage and maintaining consistent perceptual quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If VBR encoding is used to achieve constant sound quality, then perceptual quality is improved, but bitrate becomes unpredictable and may be too high or too low
Solution Approach 1:
The patent implements a feedback mechanism where the encoder monitors the actual bitrate consumption during encoding and dynamically adjusts the quantization parameters to maintain the target average bitrate. This allows the system to achieve consistent sound quality while controlling the overall bitrate within acceptable ranges.
Solution Approach 2:
The system dynamically adjusts encoding parameters between blocks of audio data, transitioning between VBR and ABR modes based on local audio characteristics and global bitrate constraints. This dynamic adaptation allows the encoder to optimize quality locally while maintaining predictable overall bitrate.
2Quantity of substance
If CBR encoding is used to maintain constant bitrate, then bitrate predictability is improved, but sound quality becomes variable and may be insufficient for complex audio
Solution Approach 1:
The audio stream is divided into small blocks that are encoded independently with locally optimized bitrate allocation. This segmentation allows the system to maintain constant overall bitrate while permitting local variations in quality based on audio complexity, ensuring adequate quality for complex passages without wasting bits on simple passages.
Solution Approach 2:
Different quantization precision is applied to different blocks of audio data based on their local characteristics. Complex audio blocks receive higher precision (more bits) while simple blocks receive lower precision (fewer bits), maintaining overall bitrate consistency while ensuring adequate sound quality where needed.
3Productivity
If psychoacoustic masking thresholds are used to determine bitrate allocation, then encoding efficiency is improved, but inaccuracies in masking models lead to suboptimal quality-bitrate tradeoffs
Solution Approach 1:
The system uses feedback from actual encoding results to refine and adjust the psychoacoustic models. By monitoring the relationship between allocated bitrate and actual perceived quality, the system adapts the masking thresholds to better match human perception, improving the accuracy of quality-bitrate tradeoffs over time.
Solution Approach 2:
The patent dynamically adjusts psychoacoustic model parameters based on local audio characteristics and encoding conditions. Rather than using fixed masking thresholds, the system modifies these parameters adaptively to better predict actual perceived quality, improving the accuracy of bitrate allocation decisions.
Data Source
AI summary
A hybrid audio encoding technique incorporates both ABR, or CBR, and VBR encoding modes. For each audio coding block, after a VBR quantization loop meets the NMR target, a second quantization loop might be called to adaptively control the final bitrate. That is, if the NMR-based quantization loop results in a bitrate that is not within a specified range, then a bitrate-based CBR or ABR quantization loop determines a final bitrate that is within the range and is adaptively determined based on the encoding difficulty of the audio data. Excessive bitrates from use of conventional VBR mode are eliminated, while still providing much more constant perceptual sound quality than use of conventional CBR mode can achieve.