avconv.c:1974: error: Integer Overflow L2
  ([0, +oo] - 1):unsigned32 by call to `avfilter_unref_buffer`.

avconv.c:1939:13: Assignment
1937.             fb->pts                 = ist->pts;
1938.             fb->buf->priv           = buf;
1939.             fb->buf->free           = filter_release_buffer;
                  ^
1940. 
1941.             buf->refcount++;

avconv.c:1974:17: Call
1972.             frame_available = ost->output_video_filter && avfilter_poll_frame(ost->output_video_filter->inputs[0]);
1973.             if (ost->picref)
1974.                 avfilter_unref_buffer(ost->picref);
                      ^
1975.         }
1976. #endif

libavfilter/avfilter.c:73:1: <LHS trace>
71. }
72. 
73. void avfilter_unref_buffer(AVFilterBufferRef *ref)
    ^
74. {
75.     if (!ref)

libavfilter/avfilter.c:73:1: Parameter `ref->buf->refcount`
  71. }
  72. 
  73. void avfilter_unref_buffer(AVFilterBufferRef *ref)
      ^
  74. {
  75.     if (!ref)

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