Low-complexity rate-distortion optimal transcoding of MPEG I-frames

The transcoding of MPEG video streams is important in a variety of situations such as in rate reduction for small bandwidth downstream channels and in extracting a fast visual playback stream for digital video cassette recorders. This paper addresses transcoding of MPEG intra-coded frames by selectively copying DCT AC coefficients from the primary MPEG stream into the secondary MPEG stream. A rate-distortion optimal transcoding approach is presented, as well as several computationally more attractive suboptimal approaches. The proposed solutions outperform the more traditional codeword extraction methods from literature.