This has all the files needed to install the background music script with added overlays!

Install Dependencies:

 sudo apt-get install omxplayer python-pygame mpg123 imagemagick python-urllib3 libpng12-0 fbi

&

 pip install requests

Just make the bash script executable with "sudo chmod +x BGM_Install.sh" and run it (NOT AS ROOT!!!) ("./BGM_Install.sh") and it will do the following:

Download stuff needed (make sure u have the dependencies above, if you have ODROID it should autodetect and install the needed ones)

Move pngview to the correct directory.

Create the /home/pi/BGM folder for music.

Add a menu item in the retropie section to enable/disable the music.

Pictures here: https://imgur.com/a/J9iek

You will still have to set up the script to run automatically when the Pi boots!: Run "sudo nano /etc/rc.local" Near the bottom, on the line above "exit 0", put the following code

 su pi -c 'python ~/BGM.py &'

Press Control+X, Y, and Enter to save changes. Reboot and enjoy! (Note: you must change "pi" to "pigaming" if you are running RetroPie on an ODROID!)

Example rc.local file: https://pastebin.com/E8NvrJJ1

Edit these to adjust the script to your needs:
###CONFIG SECTION###

startdelay = 0 # Value (in seconds) to delay audio start. If you have a splash screen with audio and the script is playing music over the top of it, increase this value to delay the script from starting.

musicdir = '~/BGM'

maxvolume = 0.75

volumefadespeed = 0.02

restart = True # If true, this will cause the script to fade the music out and -stop- the song rather than pause it.

startsong = "" # if this is not blank, this is the EXACT, CaSeSeNsAtIvE filename of the song you always want to play first on boot.

###Overlay Config###

overlay_enable = True # Enable or disable the overlay

overlay_fade_out = True # Change to "False" to have the overlay remain on the screen until an emulator/application is launched

overlay_fade_out_time = 5 # Hide the overlay after X seconds

overlay_pngview_location = '/usr/local/bin/pngview'

overlay_background_color = 'black'

overlay_text_color = 'white'

overlay_text_font = 'FreeSans'

overlay_tmp_file = '/dev/shm/song_title.png

overlay_rounded_corners = False #Set to "True" round the corners of the overlay

overlay_size = '600x32'

overlay_x_offset = '0'

overlay_y_offset = '0'

Props to Livewire for the original script: https://retropie.org.uk/forum/topic/347/background-music-continued-from-help-support

Special thanks to AndrewFromMelbourne for pngview: https://github.com/AndrewFromMelbourne/raspidmx

RetroPie forum thread: https://retropie.org.uk/forum/topic/16458/modified-background-music-script-with-added-overlays