FFmpeg graph2dot tool
I don't use Windows, but in Linux you can download the FFmpeg source, then:

cd ffmpeg
./configure
make
make tools/graph2dot


Then you can use it:

echo "nullsrc,scale=640:360,nullsink" | tools/graph2dot -o graph.tmp
dot -Tpng graph.tmp -o graph.png


Resulting in:



Not Windows specific, but maybe helpful for any Linux user who also wants to use this tool.