To create custom stereo music for Unturned, you need one main prerequisite: Unity[unity3d.com]. You need to download Unity 2019.
You also need a text reader, preferably Notepad++[notepad-plus-plus.org], though Notepad works too.

To set up this whole process, we need to do some things with Unity first. First off, of course, is to open Unity.





Next up, create a project with the button/drop-down arrow in the top-right corner. Then, name your project. The template doesn't really matter, but for familiarity's sake, make it 3D. Specify your location as wanted.









Then, wait for the project to load. It should, for the most part, look like this.









You can go ahead and delete the Scenes folder. Then, in the window where the Scenes folder was, right click, producing a context menu. Press "Import Package > Custom Package...", then navigate to "D:\Program Files (x86)\Steam\steamapps\common\Unturned\Bundles\Sources\Project.unitypackage" in your Unturned directory. Your drive (D:) will probably be different than mine, but past "Unturned\", the path should be identical. Import Project.unitypackage. It will give you checkboxes on what to import, just import everything and wait for it to load. If you go to Window > Unturned in the top left, you should see this.

The first step in this next part is importing music, which is easy enough. Find a youtube or spotify link of the song you wish to use (I use youtube for this), find a site to download an mp3 of it[ytmp3.cc] (if this site doesn't work, try this[getx.topsandtees.space] or this alternative[ytmp3.ru]), paste the share link, and download the mp3. Then, create a new folder called "Music", and drag-and-drop your music mp3 into that folder.







Then, select the music file, and navigate to the right, where you want to

• Check the "Force to Mono" checkbox
  
• Change the quality scale to about 10-30. You're aiming to make the file size at most ~2.5 MB.

Exit back out to the main folder window by clicked "Assets" in front of "Music".





Select the "Music" folder, and in the bottom right of Unity, click on "None" under "Asset Labels". Then, select "New", and type "songname.masterbundle". You can replace "songname" with the name of your song, but for simplicity's sake, only use lowercase letters (no numbers, spaces, characters, anything else). It should look like this when you're done.

Copy "Masterbundle.dat" from "Unturned > Bundles > Masterbundle.dat" and copy it into a folder. This folder is also where you are going to export your music to. I'm going to refer to this folder as MF (Mod/Master Folder). For now, MF should only have the Masterbundle.dat you just pasted in there. Open up Masterbundle.dat, which should look like this.



Change "Assets/CoreMasterBundle" representing 'Asset_Prefix' in line 5 to "Assets". After that, change "core.masterbundle" representing 'Asset_Bundle_Name' in line 1 to exactly what you named the Asset bundle for your music folder; songname.masterbundle. Once you're done, it should look like this.



Make sure that the Masterbundle.dat file you just modified is in your MF.

After you're done with that, you're ready to export. Back to Unity, select the "Music" folder, navigate to Window > Unturned > Master Bundle Tool in the top-left, click the "Asset Bundles" dropdown, check the checkbox for "songname.masterbundle", and do the same for "Multi-platform" under the "Master Bundles" dropdown if you wish. Once you're done with that, click the 3 dots icon, navigate to your MF, hit Select, then Export. After it's finished, your MF should like this. If you selected "Multi-platform", it'll make separate versions of the files for Mac and Linux.

Navigate to "Unturned\Bundles\Assets\Songs" and copy Unturned_Theme.asset. Paste it into your
MF. Rename the file to "songname.asset" or "song_name.asset". To play it safe, leave it without an underscore.




In the "songname.asset" file, start with deleting lines 10-13; the entire bracket section including the 'Namespace' and 'Token' values. After the 'Title' value, you can put your entire song name. For this example, "(Don't Fear) The Reaper". Next up, open your "songname.masterbundle.manifest". After that's done, copy the file path from line 15. Replace the pre-existing 'AssetPath' in songname.asset, "Sounds/Unturned_Theme.mp3" with what you copied. However, when pasting, remove "Assets/", so that it reads, "Music/songname.mp3". After that, replace the pre-existing 'MasterBundle' value, "core.masterbundle" with the name of the masterbundle you made. One last thing, which is technically optional, but still highly suggested (mainly for multiplayer compatibility), is to change the GUID to a new, randomized one. You can do so with this Online GUID/UUID Generator[www.guidgenerator.com]. When generating a GUID, make sure all the checkboxes for format and encoding remain unchecked. Your file should look like this when finished.

Below the brackets encompassing 'MasterBundle' and 'AssetPath', create a new line including the following:
"Link_URL" "Link"
Replace Link with any desired link, preferably a song link.

Let's check up and make sure everything is in the right format.
I'm going to use 'Paint It, Black' as an example here, for those who used their song name as the folder name for their .mp3 instead of "Music". It's perfectly fine if you used "Music" instead, just be aware of where you would see "Music" instead of the song name.



MasterBundle.dat

songname.asset

songname.masterbundle.manifest

Location of .mp3 in workspace

Master workspace

Now all your files should be ready! Open up Unturned, go to Workshop, then Submit. For collection path, it must include one subfolder. What this means is that while my MF is "D:\Custom Game Files\Unturned\Music\(Don't Fear) The Reaper", my collection path would be "D:\Custom Game Files\Unturned\Music". Having a preview image MAY be optional, but it is heavily advised, both for publicity and functionality, to have one. To submit one, just put the basic file path for the image. For example, mine will be "C:\Users\wasim\Desktop\agentsoffortune.jpg". Change note is not necessary but it is nice to have one, especially if you plan to add more songs to the mod. For the type of mod, it doesn't really matter, but for me, Item\Barricade tends to work.

Overall, this process isn't all that different from making a mod with only one song. A few things to note, however:

• You don't need separate Unity projects for this. You only need 1.
  
• Instead of naming folders for each song "Music", you should name them according to the song they represent. For simplicity's sake, I suggest naming the folders the same as you do their .asset designation.
  
• The masterbundling process SHOULD be the same process as normal.

If anything doesn't add up, no matter how minor or trivial, please tell me about it in the comments. I'll do whatever I can to help you out because this process is unnecessarily difficult and there may be inconsistencies in my guide.