This paper proposes a fast close-loop video transcoder with limited drifting error. Firstly, similar to the traditional close-loop transcoder, the proposed transcoder still accumulates the re-quantization errors of each I or P picture. However, the accumulated errors are not always introduced into the transcoding loop in every block. A triple-threshold algorithm is proposed to adaptively utilize the accumulated errors at block level so as to control drifting error under an acceptable level.

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... ndly, when the accumulated errors are not introduced into the transcoding loop, additional DCT transform in the proposed transcoder can be removed. Furthermore, the requantization process can be simply implemented by looking up table, which significantly reduces the complexity of the re-quantization process. The experimental results show that picture quality of the proposed transcoder is closed to that of the traditional closed-loop one while about 40% blocks are not updated with the accumulated errors. In this case, the transcoding process can be speeded up to 30%.