Johnnyloans audio power usage would include this.
The formula for estimating audio power usage could be one of these:
power used processing the audio file
power used processing the audio file + an estimation for how much power the speakers use.
The phone might do this 2nd formula even if you're using headphones or have the volume at 0%. (adding in speaker power even when the speakers aren't used.)
That's all correct, but the battery usage stats getting a a reset on every completed rechargeand if then the system audio shows 58% nevertheless, the battery drains rapidly and the device is warm, all in idle state, then there is a problem which isn't caused by Spotify or other possibly used playback apps.