Codec Mode Switching Compensation via Temporal Smoothing
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Solution Overview
Problem
Existing codecs face challenges in switching between different coding modes, leading to discontinuities and artifacts due to varying effective output bandwidths and energy preserving properties, particularly during transitions between blind, guided, and full-bandwidth coding modes.
Innovation Solution
Implementing temporal smoothing and blending in a high-frequency spectral band that overlaps both coding modes, allowing for seamless transitions by adjusting energy preservation properties and reducing artificial edges or jumps in the information signal's spectrogram.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switching between different coding modes (blind BWE, guided BWE, full-band core) is implemented to adapt to varying bitrate conditions, then the codec's adaptability and efficiency are improved, but discontinuities and artifacts occur at mode transitions due to different effective output bandwidths and energy preserving properties
Solution Approach 1:
The patent applies preliminary action by performing temporal smoothing and blending operations in advance during transition periods. When switching between coding modes, the system proactively applies smoothing filters and blending techniques to the high-frequency spectral band before the full effect of mode change is realized, preventing abrupt discontinuities and maintaining signal continuity throughout the transition.
Solution Approach 2:
The patent introduces an intermediary approach by creating a transition region between different coding modes. This intermediary zone uses temporal smoothing and blending as a mediator mechanism to gradually bridge the gap between modes with different effective output bandwidths and energy preserving properties, thereby reducing artifacts and maintaining signal quality during mode switching.
2Loss of energy
If blind bandwidth extension is used at low bitrates to focus available bitrate at the core-coder, then energy efficiency is improved, but significant energy attenuations occur at high frequencies compared to full-band core
Solution Approach 1:
The patent applies dynamics by making the energy preserving properties adaptive and variable rather than fixed. The system dynamically adjusts the degree of energy preservation at high frequencies based on the current coding mode and bitrate conditions. During blind BWE operation at low bitrates, the system allows greater energy attenuation at high frequencies to focus resources on the core-coder, while automatically increasing energy preservation when switching to guided BWE or full-band modes.
Solution Approach 2:
The patent changes the parameter of energy preserving properties according to the operating conditions. By varying this parameter dynamically based on the selected coding mode (blind BWE, guided BWE, or full-band core), the system optimizes the balance between energy efficiency at low bitrates and high-frequency energy preservation at higher bitrates, resolving the contradiction between these two requirements.
3Quantity of substance
If guided bandwidth extension is used at medium bitrates to synthesize wider bandwidth at higher energy, then bandwidth and energy are improved, but transitions from blind BWE or full-band core cause discontinuities
Solution Approach 1:
The patent applies preliminary action by preparing for mode transitions in advance. When the system is about to switch from blind BWE or full-band core to guided BWE, it proactively applies temporal smoothing and blending operations to the high-frequency spectral band. This preliminary preparation ensures that the transition to the wider bandwidth mode with higher energy is smooth and artifact-free, maintaining signal continuity while achieving the desired bandwidth and energy increase.
Solution Approach 2:
The patent uses temporal smoothing and blending as an intermediary mechanism to facilitate smooth transitions between coding modes with different bandwidth and energy characteristics. This intermediary technique creates a gradual bridge between the previous mode and the new guided BWE mode, eliminating discontinuities while preserving the benefits of wider bandwidth and higher energy at medium bitrates.
Data Source
AI summary
A codec allowing for switching between different coding modes is improved by, responsive to a switching instance, performing temporal smoothing and/or blending at a respective transition.