Whenever I test Minecraft and put the disc in a jukebox, the console log says:

[13:22:44] [Client thread/WARN]: Unable to play unknown soundEvent: minecraft:records.rival

 

In my main class I have:

public static Item Rival = new com.pixelmoncore.music.Rival("rival").setUnlocalizedName("discRival").setCreativeTab(tabPixelmonCoreMisc).setTextureName("pixelmoncore:record");

 

and the record class is:

public class Rival extends ItemRecord
{
	public Rival(String recordName)
	{
		super(recordName);

	}
	@SideOnly(Side.CLIENT)
	    public String getRecordTitle()
	    {
	        return "Battle - Rival";
	    }
}

 

and in the json there's...

{
"rival": {"category": "master", "sounds": [{"name": "rival", "stream": true}]}
}

 

It's probably something stupid I'm missing, but I can't figure out what I'm doing wrong..

You need to add your mod id and a colon behind the sound. It's currently looking in the Minecraft sounds for that sound.

If this is what you mean,

Rival = new com.pixelmoncore.music.Rival("pixelmoncore:rival").setUnlocalizedName("discRival").setCreativeTab(tabPixelmonCoreMisc).setTextureName("pixelmoncore:record");

 

It left me this time with:

[16:18:30] [Client thread/WARN]: Unable to play unknown soundEvent: records.pixelmoncore:rival

Try overriding getRecord() in your item and return

pixelmoncore:rival

as String