How to find the average decibels of an audio file

Im working on a procedurally generated rhythm game. A lot of the events are going to be affected by the decibels of the song. However, I need to make sure that the events happen proportionally to the decibels of the rest of the song. For example, a beat drop in one song might not be detected while another song might be identified as continuously having a beat drop. I figured the way to avoid this issue would be to find the average decibels and make these events happen proportionally to the average. However, I don't want to make the player have to sit through the entire song to calculate the average within the song, so I was wondering if there's a way I can find the average without having to play through the whole song. I already have a way of finding the decibels of a frame of a song, but I just need to know how to find the average as soon as the song is started, without having to play through the whole song.

By the way, the songs will be imported as standard audio files like mp3.