MPEG System Time Clock Locking via Pre-calculated Timestamps
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Solution Overview
Problem
In digital A/V streaming, especially with MPEG encoded Transport Streams, the absence of time base information in every Transport Packet leads to clock locking issues at startup and discontinuities in timing, affecting playback performance and requiring complex processing to restore correct timing.
Innovation Solution
A method involving a time stamp generator that calculates the System Time Clock using the first information signal packet, setting the System Time Counter to an arbitrary value and locking it with the Program Clock Reference, and generating Application Packet Arrival Time stamps to ensure accurate timing during playback and recording.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If time base information is not included in every Transport Packet, then data transmission efficiency is improved, but clock locking at startup fails and timing accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the System Time Clock value at the start of each MPEG sequence in advance. This allows the reproducing apparatus to immediately establish accurate timing reference when the sequence begins, without needing to wait for PCR signals during startup. The pre-stored STC value enables the local clock to be correctly synchronized from the very first packet, resolving the timing accuracy issue while maintaining the efficiency benefit of not embedding time base in every packet.
2Reliability
If PCR signals are transmitted regularly within Transport Packets, then clock synchronization is improved, but data transmission efficiency deteriorates due to increased overhead
Solution Approach 1:
The patent introduces an intermediary mechanism by calculating and storing the System Time Clock value as a separate preliminary parameter at the start of each sequence. This STC calculation acts as an intermediary that bridges the gap between irregular PCR transmission and the need for continuous accurate timing. The STC value serves as a pre-computed time reference that enables accurate packet timing without requiring PCR in every packet, thus maintaining clock synchronization while improving transmission efficiency.
3Adaptability or versatility
If discontinuities occur due to concatenation of different streams, then program flexibility is improved, but timing continuity deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating the System Time Clock value at the start of each concatenated stream segment. When streams are concatenated, each segment's first packet contains its pre-calculated STC value, which allows the reproducing apparatus to immediately restore correct timing reference after the discontinuity. This pre-computed timing information enables seamless timing continuity across stream boundaries, maintaining stable timing composition while preserving the flexibility to concatenate different programs.
Data Source
AI summary
Method to enable a local system time clock counter (STC) of a receiving recording device to lock to program clock reference (PCR) information comprised in a received real time sequence of information signal packets, such as MPEG2 Transport Stream packets. The method comprising determining the number of cycles between arrival of the first information signal packet and the arrival of the information signal packet comprising the first Program Clock Reference (PCR) information. This information is stored as an attribute of the stored sequence.