EgoVenture includes a streamlined way to play sound effects, music and background sounds with its Boombox singleton.
For this, EgoVenture comes with a predefined AudioBus layout, that is modified in the game's option menu and is used in the resources of the Boombox.
Hint: If you're not using the Egoventure Game Template, make sure to use addons/egoventure/default_bus_layout.tres as your default bus layout in the project settings.
See the Boombox API docs for details.
When using theBoombox.play_music function, Boombox includes an audio fader that will fade from the currently playing track to the new one.
Of course, when a game is loaded, the music and background sound that was playing in the saved game, is loaded as well.