libavcodec/vp3.c:779: error: Uninitialized Value
  The value read from motion_y[_] was never initialized.

libavcodec/vp3.c:779:25: 
777.                     frag = s->all_fragments + BLOCK_Y*s->fragment_width[1] + BLOCK_X;
778.                     if (s->macroblock_coding[current_macroblock] == MODE_INTER_FOURMV) {
779.                         SET_CHROMA_MV(motion_x[k], motion_y[k]);
                             ^
780.                     } else {
781.                         SET_CHROMA_MV(motion_x[0], motion_y[0]);
