Can't save on inserting audio through WYSIWYG

When I try to add an audio file through WYSIWYG the library opens fine and I can also select an audio file. I then click on 'submit' which takes me to the screen 'Embedding [FILENAME]', where I can select a format (which in this case doesn't make any sense). Here, the submit button doesn't work and I can't actually insert the file. The cancel button works, though.

What do I do wrong? It doesn't happen with images.