| Video transcoding is a key technology in applications of digital multimedia. Recently, it has become a study focus internationally. Transcoding is a processing technology for converting multimedia content from its original format to another suitable format, that is, to re-process the compressed stream to meet the specific needs of transmission channel and/or target decoder. H.264/AVC is a new generation video compressing standard which features high coding efficiency, flexible network adaptation, robust error resilience, and so on. Therefore, H.264/AVC can be broadly used in fields such as mobile video transmission, interactive video service and IP transmission. The great need of sharing programs between H.264/AVC and MPEG-2 systems has the research on MPEG-2/H.264 AVC transcoding becoming a new attractive topic in this area.The dissertation makes a comprehensive summarization of transcoding technology and discusses its classification in detail. This article primarily focuses on the issues and challenges associated with format transcoding from MPEG-2 to H.264. Although there are significant differences between MPEG-2 and H.264, including block shapes for motion compensation, block sizes for transformation and motion search ranges, there is still useful information available in the input MPEG-2 bit stream that can be exploited by the H.264 encoder to improve transcoding quality and reduce computational complexity. Information such as motion vector values and coding mode decisions can be reused to reduce complexity of transcoding.Coexistence of various coding standards, and the requirement for multiple resolutions and frame rates for new emerging applications, will drive the need for efficient, high-density transcoding. Transcoders are expected to progress from simple decode/re-encode devices to more complex integrated systems that reuse information in the input bit stream and achieve higher density by employing selective transform domain processing techniques. |
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