Many video transcoding architectures have been proposed to reduce the bitrates of compressed video bitstreams. Requantization of transformed coefficients (such as DCT coefficients), spatial resolution down-sampling, and temporal resolution down-sampling are the three transcoding tools which are commonly used to reduce compressed video bitrates. We propose a new video transcoding method that combines the use of different transcoding tools to transcode compressed video bit streams to various target bitrates while maintaining good subjective/objective video quality. The transcoding tools are selected based on the video content, which is characterized by two video content descriptors inferring the video spatial and motion activities, respectively. These two content descriptors can be readily computed from the compressed video bit streams without full decompression. Experimental results show that the proposed method can provide better video quality than other existing transcoders that make use of a single transcoding tool.
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