in fig2 in particular bitstream to be decoded is input on line 500 this is the same bitstream generated at the output of encoding on line 241 and enters the variable length decoder on line 501 inverse of variable length encoder 239 resulting in decoded dct coefficients on line 502 pictype signal on line 503 mbtype signal on line 504 and motion vectors on line 505 the decoded motion vectors mv on line 505 are input via lines 506 and 507 via switches 508 and 518 respectively controlled by signals 509 and 518 in b pictures depending on the mbtype mode direct prediction from a list forward prediction backward prediction and interpolated prediction either one of the switches 508 or 517 is in closed position or both are in closed position for instance if macroblock type implies forward prediction control signal 509 places switch 508 to position u2018 a u2019 likewise if macroblock type implies backward prediction control signal 518 places switch 517 into position u2018 a u2019 further when macroblock type implies interpolated prediction both switches 508 and 517 are in respective positions u2018 a u2019 thus appropriate motion vectors at least one of directs forward backward needed for the chosen macroblock type are applied via lines 511 and 520 to prev picture store 513 and the next picture store 522 prior to coding of a b picture the previous decoded picture if not a b picture available at output 535 passes via switch 537 controlled by signal 538 to line 521 and is temporarily stored in next picture store 522 and copied right over to prev picture store 513 the next picture store 522 and prev picture store 513 may also represent picture listings a and.