1. A method for coding a sequence of video frames of a mixed video stream comprising a plurality of separate videos streamed simultaneously in the sequence of video frames, each video frame in the sequence being divided into a plurality of fixed image areas, each fixed image area corresponding to one of the separate videos of the mixed video stream, the method comprising: performing a motion compensation process using motion vectors between image blocks corresponding to a number of pixels in a current image and reference blocks corresponding to a number of pixels in a reference image, said current image being divided into the plurality of fixed image areas corresponding to the plurality of separate videos, and said reference image being based on one or more images of the sequence of video frames and being divided into a plurality of reference image areas corresponding to the plurality of fixed image areas of the current image, wherein each image block is located in one of the fixed image areas of the current image, wherein each of the plurality of reference image areas corresponding to the plurality of separate videos is divided into an updated intra-coded sub-area and a non-updated intra-coded sub-area, wherein the motion compensation process includes performing, for each image block of at least a part of the current image, a temporal prediction based on a corresponding reference block indicated by a motion vector, resulting in a prediction error between the image block and the corresponding reference block, wherein said prediction error is coded; wherein for each temporal prediction of an image block located in a respective fixed image area of the current image, the reference block used for the temporal prediction is limited to pixel information only from within a partial portion of the reference image defined by (a) the respective reference image area corresponding to the respective fixed image areas of the current image, and (b) within the respective reference image area, a subset of the respective reference image area corresponding to the non-updated intra-coded sub-area of the respective reference image area.