1. Unpack yourMusic.rar or yourMusic.zip (before rename the file "yourMusic.zi" to "yourMusic.zip") in the same folder where it is.
ATTENTION!!! The path to the exe-file must be the following: True Music/media/yourMusic/AddYourMusicToTheMod.exe. Otherwise, you will get an error when launching it.

2. Place audio files in mp3, wav, ogg format in the TCBoombox and TCVinylplayer folders.

3. (optional) Place vinyl cover photos in TCVinylplayer folder in jpg format. They should be named the same as the music track file. Each music file can have its own cover.
For example, the file with the track is called "AC DC - Highway To Hell (1979).mp3", the file with the cover should be called "AC DC - Highway To Hell (1979).jpg".
The easiest way to find the cover is when you google it: "AC DC - Highway To Hell vinyl cover".

4. Run AddYourMusicToTheMod.exe. Depending on which folder the files is placed in, either a cassette or vinyl will be generated. When adding new music, you can re-run this file. 

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P.S. If you have concerns about running the exe-file, you can study its source code (files AddYourMusicToTheMod.cs, DeleteYourMusicFromTheMod.cs) and compile it yourself with a standard Microsoft .NET Framework compiler (csc.exe).