Compressed Domain Transcoding of MPEG

Current video compression formats optimize for either compression or editing. For example, motion-JPEG (MJPEG) provides excellent random access and moderate overall compression, while MPEG optimizes for compression at the expense of random access. Converting from one format to another, a process called transcoding, is often desirable over the life of a video segment. This paper shows how to transcode MPEG-1 video to motion-JPEG without fully decompressing the MPEG-1 source. The described technique for compressed domain transcoding differs from previous work because it uses a new approximation approach that is optimized for software implementations. This new approach is 1.5 to 3 times faster than spatial domain transcoders and offers an additional degree of freedom: higher transcoding speeds can be obtained at the price of lower picture quality. This speed/quality trade-off is useful in many real-time applications such as off-line editing and video gateways.