Stereo Audio Encoding for All-Zero Frame Bitrate Control
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Solution Overview
Problem
Current stereo audio encoders face inefficiencies in coding efficiency, particularly at lower bitrates, due to the impact of all-zero frames on adaptive coding statistics, leading to reduced coding efficiency for stereo parameters like residual prediction gains.
Innovation Solution
The method involves adaptive encoding of scalar quantized parameters, using Golomb-Rice encoding, and explicitly or implicitly signaling all-zero frames to control the encoding process, switching between fixed and variable rate coding based on frame conditions to optimize bit allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If adaptive coding is used for stereo parameters, then coding efficiency is improved, but all-zero frames degrade the adaptive coding statistics and reduce efficiency
Solution Approach 1:
The patent extracts and separately handles all-zero frames from the adaptive coding process. When an all-zero frame is detected, the adaptive coding statistics are preserved by not updating them with the zero values, effectively removing the harmful influence of all-zero frames on the statistical models while maintaining the benefits of adaptive coding for non-zero frames.
Solution Approach 2:
The patent performs preliminary detection of all-zero frames before they can corrupt the adaptive coding statistics. By identifying all-zero frames in advance and taking special handling measures, the system prevents the degradation of coding statistics before it occurs, ensuring continuous high efficiency in adaptive coding.
2Measurement precision
If more bits are allocated to stereo parameters, then stereo quality is improved, but bitrate consumption increases
Solution Approach 1:
The patent applies local quality by allocating bits selectively based on frame characteristics. For non-zero frames where stereo information is present, adequate bits are allocated to maintain stereo quality. For all-zero frames, no bits are wasted on stereo parameters since there is no stereo content to encode, thus optimizing the local bit allocation to match the local content requirements.
Solution Approach 2:
The patent changes the encoding parameters dynamically based on frame type. When an all-zero frame is detected, the encoding parameters for stereo parameters are adjusted to use minimal or zero bits, whereas for non-zero frames, full stereo encoding parameters are applied. This parameter adaptation allows the system to maintain stereo quality when needed while minimizing bitrate consumption when stereo content is absent.
3Device complexity
If fixed rate coding is used, then bit allocation is simplified, but coding efficiency decreases compared to variable rate coding
Solution Approach 1:
The patent segments the coding process into distinct modes: fixed rate coding for all-zero frames and variable rate adaptive coding for non-zero frames. This segmentation allows the system to use the simpler fixed rate approach when appropriate (reducing complexity) while employing the more efficient variable rate approach when needed (improving productivity), thus resolving the contradiction between simplicity and efficiency.
Data Source
AI summary
A method comprising: receiving at least two audio channel signals; determining, for a first frame, at least two parameters representing a difference between the at least two channel audio signals; scalar quantising the at least two parameters to generate at least two index values; adaptively encoding an initial scalar quantized parameter of the at least two parameters; determining whether the initial scalar quantized parameter has a value different from a predetermined value; adaptively encoding any unencoded scalar quantized parameters where the initial scalar quantized parameter has a value different from the predetermined value; determining whether all of the at least two scalar quantized parameters have values equal to the predetermined value where the initial scalar quantized parameter has a value equal to the predetermined value; adaptively encoding any unencoded scalar quantized parameters and generating an indicator that an output is one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and at least one of the at least two scalar quantized parameters have values different from the predetermined value; generating an indicator that the output is the other of the one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and all of the at least two scalar quantized parameters have values equal to the predetermined value; generating a single channel representation of the at least two audio channel signals dependent on the at least two parameters; and encoding the single channel representation.