Frédéric Devernay wrote a doc for the WriteFFmpeg Node and some recommended options at http://natron.readthedocs.io/…/fr.inria.openfx.WriteFFmpeg.…. Please take the time out a read it for your understanding on convenience.
your URL/link doesn't work.
I am sorry. Load the WriteFFmpeg node and click on the "?" in the node's setting panel.
i think, this could be the correct URL:https://natron.readthedocs.io/en/master/plugins/fr.inria.openfx.WriteFFmpeg.html
Correct!!. Sorry for the wrong link.