I\'m working on a web application that manages VRML files. I also want to let users see the uploaded files, without requiring a specific plug-in or player. X3DOM allows viewing
If you simply want to convert X3D XML encoded files to VRML Classic encoded files you can use Titania, http://titania.create3000.de/. Open your .x3d file and save it as .x3dv or .wrl.
Titania also comes with a command line utitity »x3dtidy« that can do the conversion too.