You know what's funny?
Almost there!I saw a video on that the other day from someone that was apparently riding on the log behind them (I haven't clicked the link so maybe that is the source). Unfortunately since it was headphones we couldn't hear what they were listening to and there was enough distance that you couldn't make out the track names on the device (but would they really just make those obvious?)
The guy in the video did mention that it's not necessarily that they have the final audio (maybe just some ideas or a work in progress). For all we know they could have just been listening to tracks from the movie that they felt would go in certain scenes.