I use this 'app' everyday when I go for a jog. I don't have to interact with my phone everytime a song is obnoxiously loud or inaudibly soft. With this 'app', my phone automatically adjusts the volume for me!
Only set the prefered volume of a song once and every other time it plays(on this 'app'), the phone will remember! Runs on any python console for Android such as 'qpython'.
No coding knowledge necessary! Just download the files and launch!
Use of Qpython (2.7 version) Recommended.
If you want to run this in a python 3 environment just add brackets the print functions and the raw_input function just needs to be changed to the input function.