An efficient caption insertion scheme for MPEG video in MC-DCT compressed domain

The (cinema) caption processing that adds descriptive text)It it sequence o f frames is an important video manipulation function that a video editor sh ould support. This paper proposes an efficient MC-DCT compressed domain app roach to insert the caption into tho MPEG compressed video stream. It basic ally adds the DCT blocks of the caption image to the corresponding DCT bloc ks of the input frames out, by one in the MC-DCT domains in [6]. However. t he strength of the caption image is adjusted in the DCT domain to prevent t he resulting DCT coefficients, front exceeding tit(, maximum value allowed in MPEG. In order to adjust the strength of the caption image adaptively we need to know the exact pixel value of the input image. This is a difficult task in DCT domain. We propose an approximation scheme for the pixel value s in which the DC value of a block is used as the expected pixel value for all pixels in that block Although this approximation may lead to some error s in the caption area, it still provides a relatively high image quality in the non-caption area. whereas the processing time is about 4.9 times faste r than the decode-captioning-reencode method.