Video Audio Transmission System Clock Synchronization
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Solution Overview
Problem
Existing video/audio transmission systems face challenges in synchronizing the clock frequencies of Program Clock Reference (PCR) and Coordinated Universal Time (UTC) during conversion from MPEG-2 TS to MMT, leading to potential buffer overflow and buffer depletion in decoding devices, and difficulties in GOP synchronization across dispersed encoding devices due to clock deviations.
Innovation Solution
A video/audio transmission system that generates a genlock signal using absolute time to synchronize the clock frequencies of PCR and UTC, and performs GOP synchronization by calculating a common GOP border time point across devices, ensuring accurate timestamp conversion and alignment of frame periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MPEG-2 TS is converted to MMT for transmission, then transmission efficiency and IP compatibility are improved, but clock synchronization between PCR and UTC becomes difficult to maintain
Solution Approach 1:
The patent introduces an absolute time value as an intermediary reference that mediates between the PCR clock system and UTC. This absolute time serves as a common reference point that allows conversion between the two time systems without direct coupling, thereby maintaining synchronization reliability while enabling efficient MMT transmission.
Solution Approach 2:
The patent transforms the time reference parameter from relative PCR-based timing to absolute UTC-based timing. By changing the time reference parameter and introducing absolute time values, the system achieves both transmission efficiency improvement and clock synchronization maintenance simultaneously.
2Device complexity
If dispersed encoding devices operate independently, then device complexity is reduced, but GOP synchronization across devices becomes difficult to achieve
Solution Approach 1:
The patent creates a common time reference level across all dispersed encoding devices by using absolute time values. This equipotential time reference allows each device to operate independently while maintaining synchronized GOP boundaries, as all devices reference the same absolute time for their encoding operations.
Solution Approach 2:
The absolute time value serves as a universal reference that functions across multiple dispersed encoding devices simultaneously. This universal time reference enables GOP synchronization without requiring complex inter-device communication or coordination mechanisms, allowing each device to maintain simplicity while achieving collective synchronization.
3Object-affected harmful factors
If buffer size is increased to prevent overflow, then buffer overflow is prevented, but buffer depletion and latency increase
Solution Approach 1:
The patent implements feedback control by continuously monitoring the absolute time values and adjusting the buffer management accordingly. The system uses the absolute time reference to dynamically control buffer operations, preventing overflow while optimizing buffer usage to minimize latency and avoid depletion.
Data Source
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AI summary
An object is to provide a video audio transmission system, a transmission method, a sending device, and a reception device capable of avoiding buffer overflow and buffer depletion in a decoding device and realizing GOP synchronization in encoding devices by eliminating clock deviation among devices. In the video audio transmission system according to the present invention, all of the sending devices supply clocks generated from common time point information to cameras as genlock signals. All of the reception devices supply clocks generated from the common time point information to the decoding devices as genlock signals. Therefore, clock deviation between the devices can be eliminated, and the buffer overflow and the buffer depletion in the decoding device can be avoided. Frame periods of video signals output by a plurality of dispersed cameras can be aligned, and reliable GOP synchronization can be realized by the encoding devices on a latter stage with respect to the cameras.