LOOK NO FURTHER
ITS THE SIMPLEST FIX I HAVE FOUND FOR THIS!
No need to install Xposed / Wanam Xposed.
The fix can be done right on your phone.
NOTE: This worked for me on a costom rom. Wicked v8_4.2.2
I do Not know if this works on a srock rom without root. I have not tested.
Open stock music app
Hit menu key and select settings.
Make sure you select a check mark for Smart Volume
This removed my unsafe volume warning from all my music apps including: youtube
And music app of course
NOTE: I had to do this twice to make it stick for all music apps.
Just uncheck and recheck smart volume again.
Then your finished I hope this helps!!
Sent from my SGH-M919 using xda app-developers app