libavcodec/vp3.c:765: error: Uninitialized Value
  The value read from motion_y[_] was never initialized.

libavcodec/vp3.c:765:21: 
763.                 } else {
764.                     motion_x[1] = motion_x[0];
765.                     motion_y[1] = motion_y[0];
                         ^
766.                 }
767.                 motion_x[0] = (motion_x[0]>>1) | (motion_x[0]&1);
