Research On The Digital Video/audio Splitting And Merging Technology

The splitting and merging technology for video material has been more and more widely applied with the development of digital video/audio compression and the enhancement of various multimedia services. This dissertation will focus on the algorithms and implementations of splitting and merging for video/audio from two specific points of view, material editing and cluster transcoding.In the material editing environment, the splitting and merging implementation will place its emphasis on how to implement the'cut'and'splice', known as nonlinear editing operations, on certain video/audio materials. Aiming at P2, current mainstream formats of HD nonlinear editing, the splitting and merging implementation for high rate MXF file and low rate MP4 file will be discussed in succession. For intra-frame compressed MXF files of DV and AVCI formats, the key of the implementation lies on the analysis and record of metadata and efficiency for large files. The process of metadata analyzing and video/audio data location for this kind of materials are introduced in detailed. Multi-thread file I/O scheme is proposed to reduce time-consuming, the experiments are conducted on rewriting block size and the appropriate size is suggested. For inter-frame compressed low rate MP4 files, the frame type transforming based scheme is proposed to reach the frame precision of operations for both low-delay and B-frame contained cases. Compared with the traditional schemes, it has following advandtages: reducing time-consuming dramatically due to avoiding the process of decoding and reencoding whole file; preventing video frames from quality degradation introduced by reencoding.In the cluster transcoding environment, the splitting and merging implementation will focus on splitting video/audio materials in multiple granularity, merging split clips into a smooth and integrated one, which guarantees the cluster transcoding system can effectively collect computing resources and accomplish tasks efficiently. In consideration of the service process characteristic of cluster transcoding system, the dissertation first analyzes the shortage of the physical splitting scheme and a quasi-splitting scheme based on point recording is proposed to adapt the services process of cluster system. The detailed discussion on the demultiplexing and task splitting schemes for MPEG-2 transport stream will be conducted, the splitting strategy based on GOP (Group of Pictures) is determined. Then the dissertation discusses the video/audio clips merging and multiplexing algorithms to guarantee the resynchronization between video and audio data in detailed. Finally, in the environment of cluster system which has 7 computing nodes the experiments are conducted to research the impact of splitting granularity on the performance of cluster transcoding.