A method and an encoder for encoding a video stream in a video coding format supporting auxiliary frames, where such auxiliary frames, in conjunction with the frames that reference the auxiliary frames, can be used to for rate control, in that the image data of the auxiliary frames comprises a down scaled version of an image data captured by a video capturing device, and that motion vectors of the frame referring to the auxiliary frame are calculated/determined to scale up the down scaled version of the image data to again have the intended resolution.