Originally posted by theserenitysystem:

So the 'Default' soundtrack is a custom soundtrack mod without support for the Soundtrack Menu. The way the menu is set up, you can have one of these and it'll still work great!
Your Default soundtrack could be anything though, so if you want the Jukebox to show it, you have to set it up on your end. It's pretty easy, here's how:

In the Jukebox mod folder ({your TBOI installation folder}/mods for windows users) open 'titles.lua' in your preferred text editor.

All you need are the top two entries: DefaultTitle, and Default.
Replace the word Rebirth with the title of whatever soundtrack you currently have set. It should still be in quotation marks, followed by a comma.

Inside the curly brackets for Default, put the track list for the soundtrack. Each track title must be inside quotation marks, and followed by a comma. And, in order for the Jukebox to show the right title for the soundtrack, they must be in this order:

Default = { "Basement", "Cellar", "Burning Basement", "Caves", "Catacombs", "Flooded Caves", "Depths", "Necropolis", "Dank Depths", "Womb/Utero", "Scarred Womb", "Blue Womb", "Sheol", "Cathedral", "Dark Room", "Chest", "Void", "Library", "Devil Room", "Angel Room", "Shop", "Arcade", "Secret Room", "Boss Room (Empty)", "Challenge Fight", "Boss Fight", "Boss (Alternate)", "Boss (Mom)", "Boss (Mom's Heart)", "Boss (Isaac)", "Boss (Satan)", "Boss (The Lamb)", "Boss (??? - Blue Baby)", "Boss (Hush)", "Boss (Ultra Greed)", "Boss (Delirium)", "Boss (Mega Satan)", "Devil Room Appear Jingle", "Angel Room Appear Jingle", "Secret Room Find Jingle", "Treasure Room Entry 1 Jingle", "Treasure Room Entry 2 Jingle", "Treasure Room Entry 3 Jingle", "Treasure Room Entry 4 Jingle", "Challenge Start Jingle", "Challenge Finish Jingle", "Boss Intro Jingle", "Boss Death Jingle", "Boss Death (Alternate) Jingle", "Boss Death (Hush) Jingle", --Repentance exclusive "Utero", "Downpour", "Dross", "Mines", "Ashpit", "Mausoleum", "Gehenna", "Corpse", "Home", "Abandoned Mineshaft", "Mineshaft Escape", "Planetarium", "Super Secret Room", "Ultra Secret Room", "Boss Rush", "Boss Rush (jingle)", "Boss Room (empty, twisted)", "Mom's Shadow Intro", "Strange Door (jingle)", "Echoes Reverse", "Boss (alternate alternate)", "Boss (Mother)", "Dogma Intro", "Boss (Dogma)", "Boss (Beast)", "Boss Death Alternate Alternate (jingle)", "Boss Mother Death (jingle)", "Boss Dogma Death (jingle)", "Boss Beast Death (jingle)", "Downpour (reversed)", "Dross (reversed)", "Genesis (reversed)", },

If a certain track or jingle is silent, you can put the title as

"[Silent]",

and the jukebox will automatically turn off for that track.

As an example, my Default Soundtrack is The Music of Undertale mod, by RuinSmith_Hlit
(found here: https://steamproxy.net/sharedfiles/filedetails/?id=858574642 )
Here's what it looks like:

DefaultTitle = "The Music Of Undertale", --Replace this with the name of your custom soundtrack --These are the titles of the default soundtrack above. If you leave it blank, it will be automatically filled with the Rebirth track titles. If you've installed a custom soundtrack mod without Soundtrack Menu support, put the titles for the songs here! Default = { "Ruins", --Basement "Enemy Approaching", --Cellar "Another Medium", --Burning Basement "Waterfall", --Caves "Uwaa!! So Temperate \014", --Catacombs "Quiet Water", --Flooded Caves "Snowy", --Depths "It's Raining Somewhere Else", --Necropolis "CORE", --Dank Depths "Here We Are", --Womb/Utero "Here We Are", --Scarred Womb "Amalgam", --Blue Womb "Battle Against a True Hero", --Sheol "Undertale", --Cathedral "Spider Dance", --Dark Room "Death By Glamour", --Chest "Hopes and Dreams", --Void "Home", --Library "Your Best Friend", --Devil Room "Fallen Down", --Angel Room "Shop", --Shop "sans.", --Arcade "Mysterious Place", --Secret Room "Reunited", --Boss Room (Empty) "Dummy!", --Challenge Fight "Bonetrousle", --Boss Fight "Metal Crusher", --Boss (Alternate) "Heartache", --Boss (Mom) "Your Best Nightmare", --Boss (Mom's Heart) "ASGORE", --Boss (Isaac) "Song That Might Play When You Fight Sans", --Boss (Satan) "MEGALOVANIA", --Boss (The Lamb) "Spear of Justice", --Boss (???) "MEGALOVANIA", --Boss (Hush) "Megalo Strike Back", --Boss (Ultra Greed) "SAVE the World", --Boss (Delirium) "Song That Might Play When You Fight Sans", --Boss (Mega Satan) "Flowey Laugh", --Devil Room Appear "Angel Room Appear", --Angel Room Appear "Home (Music Box) (Ending)", --Secret Room Appear "Dogsong", --Treasure Room Entry 1 "Premonition", --Treasure Room Entry 2 "Spooktune", --Treasure Room Entry 3 "Dogbass", --Treasure Room Entry 4 "Challenge Start", --Challenge Start "Good Night", --Challenge Finish "Oh My...", --Boss Intro "Good Night", --Boss Death "Good Night", --Boss Death (Alternate) "Boss Death (Hush)", --Boss Death (Hush) },

Note: Copy and paste your tracklist to a separate file. When the jukebox mod updates, it'll overwrite the titles.lua file with a blank tracklist for default. I'm not sure how to get around this, so save your tracklist somewhere else so you don't have to rewrite it out all the time.

Paste your default soundtracks below, so other folks with the same setup can use it!