One would have to know the state for many of the aspects of the machine first.
1. Brightness level
2. Background apps open? What are they doing? This includes every launch-app as well.
3. What was bing used to play the music, and what is the file types? Do they require CPU intensive decoding?
4. Any other foreground applications?
5. Is Wifi and/or bluetooth running? Connected?
6. what else is running, or being used?
Anyhting that uses power to perform, including the type of audio player will have a cumulative effect on battery life. As well, what is the naure of the health of the battery?