This is an updated version of the original Simple Background Music Player from a different author that I found on this website a few months ago.  I downloaded his version, but wanted to customize it and it was not very user friendly.  I did LOTS of research to change it for my needs.

I simplified the script and put variables at the top that are much easier to change.  Also there are comments explaining each line as well as a text file listing the proper lua name of each switch, so it will be easier for you to customize to your liking.

Tested compatible with Opentx 2.0 and 2.1.  Even works with the latest 2.1.7.

It functions like a shuffle.  Every time you flip the switch a different song will play.  I call it music roulette =D  Its pretty cool.  Because when you are flying, you don't have time to pick a song.  Just keep flipping until something you like comes on!

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Instructions on modifiying mp3 files to work with Taranis.  
Download & install Audacity - free open source sound editor.
Open Audacity and drag your music file in.

Set Project Rate drop down box to 32kHz at bottom left of audacity window.

Click the drop down arrow to the left of your track (blue lines) and towards the bottom of the list click on 'split stereo to mono' 

To export, click File, Export...

Set Save as type: to other uncompressed files
then click Options... at bottom right
Header: WAV (Microsoft)
Encoding: U-law 
OK
Save

clear comments
Done!