MP3 Timer App?

[AC Question]

I'm searching for an app playing a long mp3 at specific times, and also supports long fade-in times like 30 minutes.
The problem with all existing alarm clocks is that they turn on the screen, which is unwanted, cause it drains the battery and I want the sound to play for hours.
I want to softly fade in ambient sounds in the morning to cover noise from outside waking me up.