Optimized DCT domain motion vector estimation in frame skipped transcoding

Transcoding gets trade-off between quality and computation complexity for converting one compressed video bit-stream into another compressed bit-stream. When some incoming frames are skipped for the frame-rate reduction in transcoding, the new motion vectors and the new quantized residual DCT coefficients for outgoing bitstream should be re-computed. We propose a optimized DCT domain motion vector estimation scheme (ODME) to generate the new motion vectors and to compute the new residual DCT coefficients in compressed domain. The new approach selects the motion vector with the least prediction error from 3 candidates without motion vector refinement. Experimental results show that, compared with conventional schemes, the new approach is more efficient and can get high quality.