libavcodec/proresenc.c:823: error: Buffer Overrun L1
  Offset: [4, +oo] (⇐ 3 + [1, +oo]) Size: 4 by call to `estimate_alpha_plane`.

libavcodec/proresenc.c:748:1: Parameter `td->blocks[*]`
746. }
747. 
748. static int find_slice_quant(AVCodecContext *avctx,
     ^
749.                             int trellis_node, int x, int y, int mbs_per_slice,
750.                             ProresThreadData *td)

libavcodec/proresenc.c:823:21: Call
821.         }
822.         if (ctx->alpha_bits)
823.             bits += estimate_alpha_plane(ctx, &error, src, linesize[3],
                         ^
824.                                          mbs_per_slice, q, td->blocks[3]);
825.         if (bits > 65000 * 8)

libavcodec/proresenc.c:718:18: <Offset trace>
716. 
717.     *error = 0;
718.     cur = blocks[idx++];
                      ^
719.     bits = est_alpha_diff(cur, prev, abits);
720.     prev = cur;

libavcodec/proresenc.c:718:18: Assignment
  716. 
  717.     *error = 0;
  718.     cur = blocks[idx++];
                        ^
  719.     bits = est_alpha_diff(cur, prev, abits);
  720.     prev = cur;

libavcodec/proresenc.c:704:1: <Length trace>
702. }
703. 
704. static int estimate_alpha_plane(ProresContext *ctx, int *error,
     ^
705.                                 const uint16_t *src, ptrdiff_t linesize,
706.                                 int mbs_per_slice, int quant,

libavcodec/proresenc.c:704:1: Parameter `*blocks`
  702. }
  703. 
  704. static int estimate_alpha_plane(ProresContext *ctx, int *error,
       ^
  705.                                 const uint16_t *src, ptrdiff_t linesize,
  706.                                 int mbs_per_slice, int quant,

libavcodec/proresenc.c:722:15: Array access: Offset: [4, +oo] (⇐ 3 + [1, +oo]) Size: 4 by call to `estimate_alpha_plane` 
  720.     prev = cur;
  721.     do {
  722.         cur = blocks[idx++];
                     ^
  723.         if (cur != prev) {
  724.             if (!run)
