Systems and methods are provided for calculating a motion vector for a macroblock between a reference frame and a current frame. The system includes a main processor. The system further includes a programmable video accelerator configured to receive a linked list of variable length descriptor inputs at the direction of the main processor. The descriptor inputs include the macroblock for which the motion vector is to be calculated. The video accelerator is further configured to calculate a motion vector identifying motion of the identified macroblock from the reference frame to the current frame.