Dynamic frame skipping for high-performance transcoding

Transcoding is a process of converting a previously compressed video bitstream into a lower bit-rate bistream. When some incoming frames are dropped for the frame-rate conversion in transcoding, the newly quantized DCT coefficients of prediction error need to be re-computed, which can create an undesirable complexity as well as introduce re-encoding error. In this paper, we propose new architecture of frame-skipping transcoder to improve picture quality and to reduce complexity. It is observed that re-encoding error is reduced significantly when the strategy of direct summation of DCT coefficients and the error compensation feedback loop are employed. Furthermore, we propose a frame-rate control scheme which can dynamically adjust the number of skipped frames according to the incoming motion vectors and the re-encoding error due to transcoding such that the decoded sequence can have smooth motion as well as better transcoded pictures. Experimental results show that, as compared to the conventional transcoder, the new frame-skipping transcoder is more robust, produces smaller requantization errors, and has simple computational complexity.