Decoding System Clock Recovery via PTS Synchronization
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Solution Overview
Problem
In MPEG-2 decoding systems, the absence of a Program Clock Reference (PCR) leads to asynchronous playback of video and audio signals, resulting in unsynchronized and affected reception of both signals.
Innovation Solution
A method and apparatus that recover the System Time Clock (STC) using Presentation Time Stamps (PTS) of video or audio data, monitor the difference between PTS values, and switch between synchronous and asynchronous play modes based on a threshold value, maintaining synchronization by correcting the STC using PTS data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If asynchronous play mode is adopted when PCR is unavailable, then the system can operate without PCR, but video and audio signals cannot be synchronously played
Solution Approach 1:
The patent introduces PTS (Presentation Time Stamp) as an intermediary to recover STC (System Time Clock) when PCR is unavailable. The PTS values from video or audio packets serve as a substitute reference to regenerate the system clock, enabling synchronous playback without direct PCR access. This mediator approach allows the system to bridge the gap between unavailable PCR and required synchronization.
Solution Approach 2:
The patent changes the clock reference parameter from PCR-based to PTS-based synchronization. By recovering STC using PTS values and comparing them to determine buffering or discarding of data, the system transitions from one synchronization parameter (PCR) to another (PTS), maintaining functionality under different conditions.
2Reliability
If synchronous play mode is used, then video and audio signals are synchronously played, but the system requires PCR availability
Solution Approach 1:
The patent performs preliminary STC recovery using PTS values before actual playback occurs. By pre-regenerating the system clock from available PTS data and continuously monitoring the difference between video and audio PTS values, the system prepares synchronization parameters in advance, enabling synchronous playback even when PCR is not available.
3Reliability
If PTS is used to recover STC, then synchronization can be maintained without PCR, but system complexity increases
Solution Approach 1:
The patent enables the system to self-service by using its own PTS data to recover STC. Instead of requiring external PCR references, the system utilizes the PTS values already present in its received video or audio packets to regenerate the system clock, making the synchronization mechanism self-contained and reducing external dependencies.
Data Source
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AI summary
A method and an apparatus for processing video and audio data received in a decoding system are provided. The method includes the following steps. When a program clock reference (PCR) is unavailable in the system, a system time clock (STC) is recovered by using a presentation time stamp (PTS) of video or audio data, or a linear combination result of the PTS of the video data and the PTS of the audio data. The STC is compared with the PTSs of the currently captured and audio data, and a current data processing mode is determined. A difference between the PTS of the video data and the PTS of the audio data is monitored. An absolute value of the difference is compared with a set threshold value, and when the absolute value is greater than or equal to the threshold value, an asynchronous play mode is adopted as a system play mode; otherwise, a synchronous play mode is adopted as the system play mode. Through the method and apparatus, synchronization of video signals and audio signals can be achieved when the PCR is unavailable in the decoding system.