libavcodec/pngdec.c:219: error: Uninitialized Value
  The value read from b was never initialized.

libavcodec/pngdec.c:219:9: 
217.         }
218. #define OP_AVG(x,s,l) (((x + l) >> 1) + s) & 0xff
219.         UNROLL_FILTER(OP_AVG);
             ^
220.         break;
221.     case PNG_FILTER_VALUE_PAETH:
