Video Audio Synchronization via PTS Conversion Table
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Solution Overview
Problem
Random access playback of multiplexed video and audio streams in MPEG-2 systems can lead to desynchronization due to interframe prediction encoding, where the order of decoding and display frames do not coincide, making it difficult to use PTS information for synchronized playback.
Innovation Solution
A reproduction apparatus and method that includes a demultiplexer, video decoder, audio decoder, and controller to calculate and supply a synchronization signal based on the playback time stamp of the decoded head picture, ensuring accurate synchronization of video and audio playback by determining the display head picture's playback time stamp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If random access playback is performed on a multiplexed stream at any intermediate picture, then playback flexibility is improved, but video and audio synchronization deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the correspondence relationship between random access point picture numbers and display head picture numbers in a conversion table during stream analysis. When random access occurs, the system simply looks up the pre-calculated correspondence rather than performing complex real-time calculations, enabling both flexible random access and reliable synchronization.
Solution Approach 2:
The patent introduces an intermediary conversion table that mediates between the random access point in the decoded picture order and the corresponding display head picture. This conversion table acts as a lookup mechanism that translates arbitrary access points into the correct synchronization reference points, resolving the conflict between access flexibility and synchronization reliability.
2Quantity of substance
If PTS information is attached only to random access point pictures to reduce file size, then storage efficiency is improved, but synchronization control capability deteriorates
Solution Approach 1:
The system performs preliminary analysis of the multiplexed stream to identify all random access point pictures and pre-calculates their correspondence with display head pictures. This pre-computation stores only essential synchronization information in a compact conversion table, maintaining small file size while enabling comprehensive synchronization control for any random access point.
Solution Approach 2:
The conversion table structure is designed to be self-sufficient, containing all necessary synchronization mapping information derived from the stream's inherent structure. The system uses its own pre-analyzed stream characteristics to build the conversion table, eliminating the need for external synchronization data while maintaining full synchronization capability.
Data Source
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AI summary
In a random access playback of a stream in which video and audio are multiplexed, it is difficult to playback the video and audio in synchronization. A demultiplexer 110 separates video packets, audio packets, and caption packets from the input multiplexed stream and supplies them to a video decoder 130, an audio decoder 140, and a caption decoder 150, respectively. The video decoder 130 decodes the input video packets and calculates the PTS of the display head picture according to the PTS of the decoded head picture obtained from the video stream. A clock controller 120 supplies the PTS of the display head picture as a synchronization signal to the audio decoder 140 and the caption decoder 150. The audio decoder 140 and the caption decoder 150 decode an audio access unit and a caption access unit that have the same PTS value as the display head PTS.