MPEG Transport Stream Padding for Constant Bit Rate Conversion
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Solution Overview
Problem
Digital video broadcasting (DVB) systems face challenges in converting variable bit rate (VBR) transport streams to constant bit rate (CBR) streams, which are necessary for devices with strict timing requirements, as existing technologies fail to maintain compliant program clock references and ensure consistent bit rate transmission.
Innovation Solution
A system and method that includes an input buffer to store packets and Program Clock References (PCRs), a comparator to determine complete PCR intervals, an arithmetic unit to compute and insert null packets, and a PCR restamper to ensure compliant timing, converting VBR transport streams to CBR streams by padding with null packets and restamping PCRs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If variable bit rate transport streams are transmitted to meet dynamic content requirements, then video and audio quality is improved, but timing compliance and constant bit rate requirements of receiving devices are violated
Solution Approach 1:
A conversion device is introduced as an intermediary between the VBR transmitter and CBR receiver. This device receives VBR transport streams, pads them with null packets to achieve constant bit rate, and restamps PCRs to ensure timing compliance, thereby mediating between the conflicting VBR and CBR requirements
Solution Approach 2:
The conversion device changes the bit rate parameter from variable to constant by inserting null packets. It also modifies the PCR timestamps to maintain proper timing relationships, thereby transforming the stream parameters to meet receiver requirements while preserving content quality
2Stability of the object's composition
If null packets are inserted to pad the transport stream to constant bit rate, then bit rate consistency is improved, but stream complexity and processing requirements increase
Solution Approach 1:
The padding process is segmented into discrete null packet insertions at specific positions in the transport stream. Each null packet is a standardized empty transport packet, allowing systematic and manageable insertion without requiring complex continuous modulation
Solution Approach 2:
The conversion device creates copies of the VBR stream with additional null packets inserted. The original stream structure is preserved and copied, with supplementary null packets added to achieve the target constant bit rate without fundamentally altering the existing packet format
3Measurement precision
If Program Clock References are restamped to ensure compliant timing, then timing accuracy is improved, but risk of PCR overflow or underflow increases
Solution Approach 1:
The conversion device monitors the PCR intervals and timing relationships in the input VBR stream, uses this feedback information to calculate appropriate null packet insertions, and adjusts the output PCR timestamps accordingly to maintain timing accuracy while preventing overflow or underflow conditions
Solution Approach 2:
The device performs preliminary calculation of the required null packet insertions and PCR restamping values before generating the output stream. This advance preparation ensures that timing compliance is maintained from the outset and prevents PCR timing errors before they occur
Data Source
AI summary
A system and method for processing of MPEG transport streams. Specifically, the system may receive a variable bit rate input transport stream with one or more programs. The variable bit rate transport stream is converted into a constant bit rate stream with compliant Program Clock References. Null packets are added to the transport stream at suitable locations to pad it to a constant bit rate. Program clock reference packets are re-stamped to ensure all timing requirements are met.