Unfortunately, I'm not really sure there even was pornography in 14th century france-- that would have been the 1300s. Is there a specific work you're thinking of?

Either way, pornography would not have existed as we are aware of it and call it, the concept is a relative modern one, only dating to around 1850 or so. The erotic would have been seen and known about, and it largely wasbused as a mode of talking about the Church or the State, but I can't think of any 1300s french authors.

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Licentious writings and representations have been with us since at least the time of the Paleolithic cave painters and stone sculptors, but by its very nature, porn is the lesser, courser cousin of erotic art, and as such -- in any of its many forms, be they painting, writing, dance or song-- less likely to survive, let alone survive long enough to be celebrated.

Noted 14th century writerly exceptions include Boccacio (Italy,) and Chaucer (England,) and certainly translations of these and far earlier works by writers like Ovid would have made their way to France via monks and scholars.

Pornographic doodlings can be found in any number of medieval illuminated manuscripts (most often in the margins of books of hours,) but as these works were only owned by the extremely wealthy, (the most famous collector of which was the French prince John, Duke of Berry; 1340–1416) it was not until the invention of the printing press in around 1440 that any sort of mass circulation of erotica (in Europe, at least,) was possible. So as you note, porn-- particularly in 14th century France-- was very likely the same underground, individualized commodity it was until relatively recently.