A method of global motion estimation between frames of a motion compensated inter-frame encoded video sequence, in which each particular frame of the sequence has a plurality of motion vectors encoded therein relating the particular frame to a further frame of the sequence, in which the further frame precedes or succeeds the particular frame in the sequence; the method comprising: a) determining a motion estimation representative of the global motion between the particular frame and the further frame on the basis of motion vectors therebetween, characterised in that the method comprises: b) determining one or more further motion estimations representative of the global motion between the particular frame and the further frame by means of: (i) determining one or more motion estimations representative of the global motion of the particular frame with respect to one or more other frames, in which the one or more other frames precede or succeed the particular frame in the sequence; (ii) determining one or more motion estimations respectively representative of the global motion of the one or more other frames with respect to the further frame, and (iii) accumulating the respective motion estimations determined in steps (i) and (ii) to give one or more respective overall motion estimations, each motion estimation substantially representative of the global motion of the particular frame with respect to the further frame; and c) selecting one of the motion estimations determined in steps (a) and (b) which meets at least one predetermined criterion as being representative of the global motion of the particular frame; wherein the selecting step c) further comprises: (iv) testing the motion estimations in turn, in which the test comprises comparing the median error value of a motion estimation with a threshold median error value, the test being passed if the median error value of the motion estimation does not exceed the threshold value; and (v) outputting a motion estimation as being representative of the global motion of the frame if it passes the test, wherein the test is applied in turn to motion estimations once they have been determined, and if the test is passed then no further motion estimations are determined. a) determining a motion estimation representative of the global motion between the particular frame and the further frame on the basis of motion vectors therebetween, characterised in that the method comprises: b) determining one or more further motion estimations representative of the global motion between the particular frame and the further frame by means of: (i) determining one or more motion estimations representative of the global motion of the particular frame with respect to one or more other frames, in which the one or more other frames precede or succeed the particular frame in the sequence; (ii) determining one or more motion estimations respectively representative of the global motion of the one or more other frames with respect to the further frame, and (iii) accumulating the respective motion estimations determined in steps (i) and (ii) to give one or more respective overall motion estimations, each motion estimation substantially representative of the global motion of the particular frame with respect to the further frame; and (i) determining one or more motion estimations representative of the global motion of the particular frame with respect to one or more other frames, in which the one or more other frames precede or succeed the particular frame in the sequence; (ii) determining one or more motion estimations respectively representative of the global motion of the one or more other frames with respect to the further frame, and (iii) accumulating the respective motion estimations determined in steps (i) and (ii) to give one or more respective overall motion estimations, each motion estimation substantially representative of the global motion of the particular frame with respect to the further frame; and c) selecting one of the motion estimations determined in steps (a) and (b) which meets at least one predetermined criterion as being representative of the global motion of the particular frame; (iv) testing the motion estimations in turn, in which the test comprises comparing the median error value of a motion estimation with a threshold median error value, the test being passed if the median error value of the motion estimation does not exceed the threshold value; and (v) outputting a motion estimation as being representative of the global motion of the frame if it passes the test, wherein the test is applied in turn to motion estimations once they have been determined, and if the test is passed then no further motion estimations are determined.