The standard GOP length of e.g. a MPEG sequence for DVDs is max. 15 images. Such a fixed GOP structure has a lot of disadvantages for CCTV applications. If there is a lot of motion in the camera images, the size of the difference pictures increases as long as the next I-frame is generated. If there is less motion in the camera images, many I-frames (reference pictures) are generated due to the GOP structure although this is not needed, the required storage capacity is increased considerably. MPEG4CCTV offers dynamic GOP length control which automatically generates a new I-frame if the camera image changes considerably, or, if there is less motion, which keeps generating difference images (B-frames, referring to the previous I-frame) for a considerably longer period of time.