libavcodec/proresenc.c:822: error: Buffer Overrun L1
  Offset: [4, +oo] (⇐ 3 + [1, +oo]) Size: 4 by call to `estimate_alpha_plane`.

libavcodec/proresenc.c:747:1: Parameter `td->blocks[*]`
745. }
746. 
747. static int find_slice_quant(AVCodecContext *avctx,
     ^
748.                             int trellis_node, int x, int y, int mbs_per_slice,
749.                             ProresThreadData *td)

libavcodec/proresenc.c:822:21: Call
820.         }
821.         if (ctx->alpha_bits)
822.             bits += estimate_alpha_plane(ctx, &error, src, linesize[3],
                         ^
823.                                          mbs_per_slice, q, td->blocks[3]);
824.         if (bits > 65000 * 8)

libavcodec/proresenc.c:717:18: <Offset trace>
715. 
716.     *error = 0;
717.     cur = blocks[idx++];
                      ^
718.     bits = est_alpha_diff(cur, prev, abits);
719.     prev = cur;

libavcodec/proresenc.c:717:18: Assignment
  715. 
  716.     *error = 0;
  717.     cur = blocks[idx++];
                        ^
  718.     bits = est_alpha_diff(cur, prev, abits);
  719.     prev = cur;

libavcodec/proresenc.c:703:1: <Length trace>
701. }
702. 
703. static int estimate_alpha_plane(ProresContext *ctx, int *error,
     ^
704.                                 const uint16_t *src, int linesize,
705.                                 int mbs_per_slice, int quant,

libavcodec/proresenc.c:703:1: Parameter `*blocks`
  701. }
  702. 
  703. static int estimate_alpha_plane(ProresContext *ctx, int *error,
       ^
  704.                                 const uint16_t *src, int linesize,
  705.                                 int mbs_per_slice, int quant,

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