I have idvd 7.1.2, and no audio shows up under the media button. I have iTunes 12.4.0 with a lot of music. How do I get audio into my start up menu?

Since iDVD has been out of development for over 2 years it is on its death bed. With each system update more of it becomes incompatible.

The only workaround I've found is to drag your iTunes folder into iDVD's Media/Audio pane. You can access the tracks there by artist.

That's about the best we can do.

We only have access to the actual audio files, not the iTunes database that contains the playlists.

However, you can select multiple tracks in the Media pane when holding down the Command key and drag them to the add music box:

I've found that the tracks will play in the order you chose them.