libavfilter/vf_crop.c:320: error: Integer Overflow L2
  ([0, +oo] - 1):unsigned32 by call to `avfilter_unref_buffer`.

libavfilter/vf_crop.c:320:5: Call
318. 
319.     crop->var_values[VAR_N] += 1.0;
320.     avfilter_unref_buffer(link->cur_buf);
         ^
321.     ff_end_frame(link->dst->outputs[0]);
322. }

libavfilter/buffer.c:74:1: <LHS trace>
72. }
73. 
74. void avfilter_unref_buffer(AVFilterBufferRef *ref)
    ^
75. {
76.     if (!ref)

libavfilter/buffer.c:74:1: Parameter `ref->buf->refcount`
  72. }
  73. 
  74. void avfilter_unref_buffer(AVFilterBufferRef *ref)
      ^
  75. {
  76.     if (!ref)

libavfilter/buffer.c:78:11: Binary operation: ([0, +oo] - 1):unsigned32 by call to `avfilter_unref_buffer` 
  76.     if (!ref)
  77.         return;
  78.     if (!(--ref->buf->refcount))
                ^
  79.         ref->buf->free(ref->buf);
  80.     if (ref->extended_data != ref->data)
