H.264 to MPEG-4 Transcoding Using Block Type Information

In this paper, we propose a heterogeneous transcoding method of converting an H.264 video bitstream into an MPEG-4 video bitstream. When the H.264 video bitstream is transformed into the MPEG-4 video bitstream, the conversions between the H.264 block types and the MPEG-4 block types are performed by minimizing the distortion, and 4times4 block-based motion vector mapping is performed. The proposed transcoder runs 5.2 times faster than the cascaded transcoding method, while maintaining the similar PSNR (peak-signal-to-noise ratio).

I. Introduction

MULTIMEDIA services for network environments, such as video communications, digital libraries and video adaptations, are becoming increasingly prevalent. In multimedia applications, it is often necessary to adapt the bitrates of the video bitstream to the bandwidths of the different kinds of communication channels. Therefore, various video transcoding techniques [1], [2] have been developed to convert one compressed bitstream format into another, while guaranteeing the QoS (quality of service). These different transcoding technologies are commonly classified according to the techniques which are used to perform the transcoding in the pixel-domain [3] and in the DCT (Discrete Cosine Transform)-domain [4]. So far, homogeneous transcoding methods have been developed to perform conversions from MPEG-2 to MPEG-2 [4] and H.263 to H.263 [5].