An Efficient H.264 Transcoder with Spatial Downscaling for Wireless Communications

Wireless video communication is an important application supported by 3G mobile communication systems. Motivated by the wide adoption of H.264 and the demand of universal multimedia data access over wireless network, this paper presents a fast video transcoder, working entirely in the DCT-domain, to convert high quality H.264 bitstream into low bit rate stream with low spatial resolution for wireless video access, furthermore, a motion vector estimation algorithm based on mapping and merging process is proposed to utilize the original motion information to predict motion vectors for the downscaled video. Simulation results show that, compared with the conventional transcoder, the proposed method significantly reduces the transcoding complexity while maintaining comparable rate distortion performance.