Media Packet Time Stamping for Synchronized Video Distribution
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Solution Overview
Problem
Existing methods for synchronizing media streams across multiple client devices in IP networks suffer from delays and asynchrony due to varying packet loss and jitter, leading to significant differences in playback timing and ruining the viewing experience, especially in real-time multimedia communication.
Innovation Solution
A method involving a central master node that provides a common master-client shared time reference, determines mean arrival times, and time-stamps packets with playout information to ensure synchronized playback across devices, using a shared time reference like UTC or NTP, and inserts time stamps directly into media packets to avoid firewall issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If buffering is used to compensate for network packet loss and jitter, then reliability of playback is improved, but delay increases
Solution Approach 1:
The system performs preliminary time stamping at the master node before distribution, calculating precise playout times in advance based on a common time reference. This preliminary action eliminates the need for extensive buffering at client devices, as packets arrive with pre-calculated timing information that enables immediate synchronized playback without delay.
2Adaptability or versatility
If Adaptive Bit Rate (ABR) switching is implemented to handle different network conditions, then adaptability is improved, but device complexity increases
Solution Approach 1:
The master node acts as an intermediary that performs time stamping and playout time calculation centrally before distribution. Client devices receive packets with pre-calculated timing information and simply play back at the specified times without needing complex ABR switching logic or buffering management, thus reducing client device complexity while maintaining adaptability.
3Stability of the object's composition
If RTP/RTCP is used for synchronization within a client device, then video-audio sync is improved, but inter-device synchronization is not achieved
Solution Approach 1:
The system uses a universal common time reference (such as UTC or GPS time) that serves multiple functions: it synchronizes video and audio within each device, and simultaneously synchronizes playback across all client devices. The time stamps embedded in packets reference this universal time, enabling both intra-device and inter-device synchronization with a single mechanism.
4Measurement precision
If time stamps are inserted into media packets for synchronization, then playout precision is improved, but network overhead increases
Solution Approach 1:
The system merges the time stamping function with the existing RTP packet structure by embedding the playout time information in the RTP timestamp field. This combining approach provides precise playout timing without requiring separate time synchronization protocols or additional packets, thus avoiding increased network overhead while maintaining high precision.
Data Source
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AI summary
There is provided a method in a distribution network (200), comprising a central master node 101 for distributing a received media stream D0 comprising packets of a first type over the distribution network to a multiple of client devices (151,152,153). The method comprising providing a common master-client shared time reference Tref, and determining a mean intermediate arrival time for received packets of the first type, which is utilized for providing playout time information for the packets together with the time reference Tref.