PNG_FILTER_VALUE_SUB  194 libavcodec/pngdec.c     case PNG_FILTER_VALUE_SUB:
PNG_FILTER_VALUE_SUB  124 libavcodec/pngenc.c     case PNG_FILTER_VALUE_SUB:
PNG_FILTER_VALUE_SUB  151 libavcodec/pngenc.c         pred = PNG_FILTER_VALUE_SUB;