Researches On MPEG-2 To H.264/AVC Video Transcoding And Relative Techniques

MEPG-2 and H.264/AVC are the most important video encoding standards. The fact that the streams encoded with MPEG-2 standard need to be decoded on the H.264-based terminals and the coexistence of these two standards makes the transcoding from MPEG-2 to H.264 the hot topic in the video transcoding field. Different kinds of applications have different requirements on MPEG-2/H.264 transcoding. For example, the service providers of the TV broadcasting would like to transmit more programs on limited width channels, and the stream multimedia screams for real-time multimedia signals. Since traditional H.264 encoding process intends to obtain the best RD performance in spite of complexity, and MPEG-2 motion estimation results are good indications for H.264 motion estimation, the key problem of MPEG-2/H.264 transcoding is how to use the information obtained in MPEG-2 decoding process to simplify the H.264 encoding.The main contributions of this thesis are as follows:(1)An improved MPEG-2/H.264 intra transcoding algorithm is proposed firstly. The reference algorithm of the proposed is one of the simplest algorithms among MPEG-2/H.264 intra transcoding solutions. It determines the re-encoding mode by calculating the variance of MPEG-2 DC coefficients and determines the H.264 prediction mode by using the relationship of MPEG-2 horizontal and vertical AC coefficients. The reference algorithm determines both the H.264 mode and prediction mode at one time, which avoid the high complexity of traditional H.264 encoding process. However, the theoretic foundation of the reference algorithm has little flaw, which causes the incomplete coverage in prediction mode determination. The proposed algorithm re-analyzes and improves the theoretic foundation of the reference algorithm. The experimental results show that the improved solution obtains a better RD performance without adding any complexity.(2) A fast MPEG-2/H.264 inter transcoding algorithm is also proposed. In this thesis, the relationship of MPEG-2 residual DCT coefficients and the H.264 encoding modes is analyzed. Besides, the relationship of MPEG-2 MV/PMV and H.264 motion estimation center/range is analyzed. The proposed algorithm reduces 2/3 complexity and the PSNR almost keeps the same, with the cost of bitrate increase of 5.7%. The most important is that the proposed algorithm needs no preset or posterior thresholds or parameters, which are very preferable to real-time transcoding applications.(3) Considering the fact that MPEG-2/H.264 transcoding is always companied with frame skipping, the research on frame-skipping transcoding is also studied. In this thesis, a frame-skipping transcoding scheme based on periodical constraint and dynamic frame-skipping decision is proposed. Periodical constraint makes the transcoded stream more logical, and the dynamic skipped frame selection re-encodes the frames with more activity information, which is always the most expected information for people. In this proposed algorithm, dropping one frame or not is decided by the frame activity. The frame activity is predicted according to the activities of the previous two frames ahead of time, which is very useful for real-time transcoding. In the proposed frame-skipping transcoding scheme, multi-frame skipping may happen. A new overlapping block location algorithm is also proposed for MV reconstruction in multi-frame skipping process to reduce the drift error occurred in the traditional solution. The efficiency of the proposed algorithm is better than that of the traditional one, and its advantages are more obvious as the number of skipping frames is increased. According to the proposed frame-skipping transcoding scheme, the corresponding architecture is also proposed for hardware design.(4) The decoding of H.264 is one of the most important stages of the MPEG-2/H.264 transcoding system, which plays an important role for real-time transcoding application. In this thesis, a parallel decoding architecture with double controllers is proposed to meet the above requirement. To improve the time and storage efficiency in this entropy decoder, the main controller, the sub controller, the storage of context parameters and the central decoder are optimized according to the characters of the decoding objects, i.e. the syntax elements (SEs). Experimental results show that the proposed architecture saves 27.9%, 18.2% and 48.8% of the decoding time compared with the reference decoder in I frame, P frame and B frame, respectively.