1. A computerized method for transcoding a sequence of input images, each one of the input images comprising input macroblocks of pixels encoded in a first format, into a sequence of output images, each one of the output images comprising output macroblocks of pixels encoded in a second format, the method comprising: transcoding in a computer having a processor, comprising: reading a set of transcoding use cases, comprising two or more transcoding use cases, wherein each transcoding use case is characterized by a respective type of adaptation to be performed on an input image of the sequence of input images; decoding input macroblocks of the input image, comprising extracting metadata comprising encoding block modes and determining partitions and respective motion vectors, thereby decoding the input image into a decoded input image; based on the set of transcoding use cases, determining a number of stages for mapping motion vectors; performing transcoding operations on the decoded input image using the extracted metadata, the transcoding operations corresponding to the set of transcoding use cases and comprising mapping motion vectors to generate an adapted input image, each transcoding operation corresponding to a transcoding use case in the set of transcoding use cases; and re-encoding the adapted input image to generate a corresponding output image of the sequence of output images.