Stream Playback Speed Control for IP Packet Timing Mismatch
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Solution Overview
Problem
Existing VoIP techniques struggle to maintain speech quality during playback over IP networks due to unsynchronized internal clocks between transmission and reception terminals, leading to issues like sound skipping and delay, especially when packet arrival timing and order are not guaranteed.
Innovation Solution
A stream data reception/playback apparatus with a receiving section, synchronization difference calculation section, frame detection section, and playback speed control section that adjusts playback speed based on synchronization differences and frame detection, interpolating or decimating data to stabilize buffer content and reduce quality deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed amount of received packets is periodically extracted from a buffer using the receiving side's internal clock, then speech playback can be performed, but quality deterioration such as breaks or sound skipping occurs due to clock frequency differences between transmission and reception sides
Solution Approach 1:
The patent makes the packet extraction amount dynamic by adjusting it based on the detected clock frequency difference. Instead of extracting a fixed amount of packets, the extraction amount varies according to the synchronization status between transmission and reception clocks, thereby adapting the playback process to compensate for clock frequency mismatches and prevent quality deterioration
Solution Approach 2:
The patent implements a feedback mechanism where the receiving side detects the transmission side's clock frequency and uses this information to adjust the packet extraction amount. This closed-loop control continuously monitors synchronization status and modifies playback parameters accordingly, ensuring stable speech quality despite clock differences
2Reliability
If the buffer capacity is increased to prevent sound skipping, then speech quality can be maintained, but delay in played back speech increases gradually
Solution Approach 1:
The patent changes the parameter of packet extraction amount dynamically based on clock frequency difference detection. By adjusting this parameter in real-time, the system maintains adequate buffer utilization without requiring excessive buffer capacity, thus preventing both quality deterioration and excessive delay
3Reliability
If dynamic adjustment of receiving side's internal clock frequency is performed using transmission side's clock as reference, then speech quality can be maintained, but circuit scale increases
Solution Approach 1:
The patent extracts only the essential function of clock frequency difference detection and uses this information to control packet extraction amount. Instead of implementing full clock synchronization with dynamic frequency adjustment, the invention isolates the critical measurement function and applies its results to the playback control, thereby reducing circuit complexity while maintaining speech quality
Data Source
AI summary
There is disclosed a stream data reception/reproduction device capable of suppressing deterioration of quality of stream data reproduced even when the stream data is received via an IP network or the like in which the packet arrival timing and the order are not guaranteed. In this device, a reproduction speed control unit (107) sets various conditions in accordance with the value of the synchronization difference reported from a synchronization difference calculation unit (102). Only when the set conditions are satisfied, the speed of reproduction of a frame decompressed and inputted from a decoding unit (105) is adjusted. The reproduction speed control unit (107) interpolates a predetermined amount of sample data into the frame or decimates it from the frame when adjusting the reproduction speed.