In video transcoding, useful coding statistics become available when the input video stream is decoded. It is possible to utilize these statistics to improve the transcoding performance. In this paper we investigate how to use these statistics to perform the picture bit-allocation for transcoding a pre-encoded video bit-stream. We propose a scheme to estimate the complexities of the pictures of the output video using the coding statistics computed from the input video stream. Based on the estimated picture complexity, we present a picture bit-allocation algorithm for the rate-control of the transcoding process. The algorithm is simple to compute, and effectively improves the video quality and reduces the picture quality variations.
Most previous research efforts on video transcoding have been focused on changing the bit-rate of one pre-encoded bit-stream to another. However, in many applications (e.g. streaming video over a heterogeneous network), it may require to transcode a pre-encoded video bit-stream to multiple bit-streams with different bit-rates and features to support multiple clients with different requirements. In this paper, we discuss the case of point-to-multipoint transcoding. We compare two transcoder architectures in terms of processing speed for H.263 and MPEG-2 transcoding. We show that for point-to-multipoint transcoding, a cascaded video transcoder is more efficient since some parts of the transcoder can be shared by the multiple clients.
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