libavcodec/pngdec.c:207: error: Uninitialized Value
  The value read from b was never initialized.

libavcodec/pngdec.c:207:13: 
205.         } else {
206. #define OP_SUB(x,s,l) x+s
207.             UNROLL_FILTER(OP_SUB);
                 ^
208.         }
209.         break;
