A method comprising: computing a motion vector predictor for a current field motion vector for a current field of a current macroblock in an interlaced frame coded picture, said computing a motion vector predictor comprises: determining a number of one, two or three valid candidate motion vectors for predicting a field motion vector for the current field of the current macroblock in the interlaced frame coded picture; for each of the one, two or three valid candidate motion vectors, determining the field polarity of the reference frame referred to by the valid candidate motion vector; calculating the motion vector predictor for the field motion vector based at least in part on the field polarities of the one, two or three valid candidate motion vectors, wherein the calculating comprises: determining the motion vector predictor depending on the number of valid candidate motion vectors, the number of same field candidate motion vectors and the number of opposite field candidate motion vectors, the same field candidate motion vectors referring to the same field relative to the polarity of the current field, the opposite field candidate motion vectors referring to the opposite field relative to the polarity of the current field, including, when the number of valid candidate motion vectors is three: if the number of same field candidate motion vectors is three or the number of opposite field candidate motion vectors is three, computing a median of the valid candidate motion vectors, otherwise, if the number of same field candidate motion vectors is greater than or equal to the number of opposite field candidate motion vectors, selecting one of the same field candidate motion vectors, and otherwise, selecting one of the opposite field candidate motion vectors; and if the number of valid candidate motion vectors is less than three, the calculating comprises selecting one of the valid candidate motion vectors to use as the motion vector predictor without performing the median operation on the valid candidate motion vectors. determining a number of one, two or three valid candidate motion vectors for predicting a field motion vector for the current field of the current macroblock in the interlaced frame coded picture; for each of the one, two or three valid candidate motion vectors, determining the field polarity of the reference frame referred to by the valid candidate motion vector; calculating the motion vector predictor for the field motion vector based at least in part on the field polarities of the one, two or three valid candidate motion vectors, wherein the calculating comprises: determining the motion vector predictor depending on the number of valid candidate motion vectors, the number of same field candidate motion vectors and the number of opposite field candidate motion vectors, the same field candidate motion vectors referring to the same field relative to the polarity of the current field, the opposite field candidate motion vectors referring to the opposite field relative to the polarity of the current field, including, when the number of valid candidate motion vectors is three: if the number of same field candidate motion vectors is three or the number of opposite field candidate motion vectors is three, computing a median of the valid candidate motion vectors, otherwise, if the number of same field candidate motion vectors is greater than or equal to the number of opposite field candidate motion vectors, selecting one of the same field candidate motion vectors, and otherwise, selecting one of the opposite field candidate motion vectors; and if the number of valid candidate motion vectors is less than three, the calculating comprises selecting one of the valid candidate motion vectors to use as the motion vector predictor without performing the median operation on the valid candidate motion vectors. if the number of same field candidate motion vectors is three or the number of opposite field candidate motion vectors is three, computing a median of the valid candidate motion vectors, otherwise, if the number of same field candidate motion vectors is greater than or equal to the number of opposite field candidate motion vectors, selecting one of the same field candidate motion vectors, and otherwise, selecting one of the opposite field candidate motion vectors; and if the number of valid candidate motion vectors is less than three, the calculating comprises selecting one of the valid candidate motion vectors to use as the motion vector predictor without performing the median operation on the valid candidate motion vectors.