AV Data Synchronization Using PTP Time Markers
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Solution Overview
Problem
Television broadcasting faces challenges in synchronizing the frequency and phase of decoders in media devices with a master media timing source due to propagation delays and varying clock rates and phases across multiple audio and video feeds, with existing techniques like PCR and PTP being inefficient and slow to converge.
Innovation Solution
A method involving the use of precision time protocol (PTP) time stamps indexed to time markers for packetized audio video (AV) data, which are received and processed by a receiver to lock the phase of AV data, using a phase lock loop (PLL) to adjust for delays and synchronize with a master timing source, ensuring accurate synchronization across a network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional time stamp techniques (PCR, PTP) are used for synchronization, then basic timing reference is provided, but convergence speed is slow and precision is insufficient
Solution Approach 1:
The patent applies preliminary action by embedding time markers directly into the AV data packets at the source before transmission. These time markers are pre-synchronized to a precise clock reference, allowing receiving devices to immediately use them for phase locking without waiting for slow convergence protocols like PTP to establish synchronization.
Solution Approach 2:
The patent implements continuous synchronization by continuously embedding time markers in every AV data packet throughout the data stream. This continuous presence of timing information allows the receiving device to continuously adjust and maintain phase lock, eliminating the intermittent updates inherent in PTP's periodic time stamping.
2Measurement precision
If multiple unique time stamps are applied to multiple audio and video feeds, then each feed can be individually timed, but device complexity increases significantly
Solution Approach 1:
The patent applies universality by using a single synchronized time marker format across all audio and video feeds. Instead of requiring multiple unique time stamping mechanisms for different feeds, the same time marker embedding approach works universally for all feeds, simplifying the timing management system while maintaining individual feed precision.
Solution Approach 2:
The patent merges the timing reference function into the existing AV data packet structure itself. By combining the time marker with the packet header or payload in a unified manner, the system eliminates the need for separate, complex timing distribution infrastructure that would otherwise be required for each individual feed.
Data Source
AI summary
The present aspects relate to techniques of timing synchronization of audio and video (AV) data in a network. In particular, the techniques for a AV master to distribute AV data encoded with one or more time markers to a plurality of processing nodes. The one or more time markers may be indexed to a precision time protocol (PTP) time stamp used as a time reference. In one technique, the nodes extract the time markers to determine an offset value that is applied to a PLL to synchronize AV data packets at a distribution node or a processing node. In another technique the distribution node or the processing node determines the worst case path, which corresponds to a system offset value. The distribution node then reports the system offset value to the AV master, which in turn adjusts the phase based on the report.