Add MP3 sound support via JLayer decoding

- build.gradle: add javazoom:jlayer:1.0.1 dependency (bundled via include())
- Mp3Decoder: new utility class that decodes MP3 to WAV using JLayer
- SplashSound: detect .mp3 files in config dir, decode to .wav for the dynamic resource pack
- Default .ogg still works; place a .mp3 file in config/justasplash/ for MP3 playback

build.gradle

@@ -35,6 +35,9 @@ dependencies {
 
     modImplementation("com.github.usefulness:webp-imageio:0.10.2")
     include("com.github.usefulness:webp-imageio:0.10.2")
+
+    modImplementation("javazoom:jlayer:1.0.1")
+    include("javazoom:jlayer:1.0.1")
 }
 
 loom {

src/main/java/net/anomaly/justasplash/splash/SplashSound.java

@@ -3,6 +3,7 @@ package net.anomaly.justasplash.splash;
 import net.anomaly.justasplash.JustASplash;
 import net.anomaly.justasplash.config.SplashConfig;
 import net.anomaly.justasplash.util.Compat;
+import net.anomaly.justasplash.util.Mp3Decoder;
 import net.fabricmc.fabric.api.resource.ResourceManagerHelper;
 import net.fabricmc.fabric.api.resource.ResourcePackActivationType;
 import net.fabricmc.loader.api.FabricLoader;
@@ -30,14 +31,17 @@ public class SplashSound {
             return;
         }
 
-        boolean hasCustomOgg;
+        boolean hasCustomSound;
         try (Stream<Path> files = Files.list(assetDir)) {
-            hasCustomOgg = files.anyMatch(p -> p.toString().endsWith(".ogg"));
+            hasCustomSound = files.anyMatch(p -> {
+                String name = p.toString().toLowerCase();
+                return name.endsWith(".ogg") || name.endsWith(".mp3");
+            });
         } catch (IOException e) {
-            hasCustomOgg = false;
+            hasCustomSound = false;
         }
 
-        if (hasCustomOgg && !packRegistered) {
+        if (hasCustomSound && !packRegistered) {
             ensurePackMeta(assetDir);
             ensureAssetStructure(assetDir);
 
@@ -71,12 +75,25 @@ public class SplashSound {
             Path soundsDir = assetDir.resolve("assets/justasplash/sounds");
             Files.createDirectories(soundsDir);
 
-            Path dst = soundsDir.resolve(soundFile);
-            if (!Files.exists(dst)) {
-                Files.copy(src, dst);
+            String dstName = soundFile;
+            if (soundFile.toLowerCase().endsWith(".mp3")) {
+                dstName = soundFile.replaceAll("(?i)\\.mp3$", ".wav");
             }
 
-            String name = soundFile.replaceAll("\\.\\w+$", "");
+            Path dst = soundsDir.resolve(dstName);
+            if (!Files.exists(dst)) {
+                if (soundFile.toLowerCase().endsWith(".mp3")) {
+                    try {
+                        Mp3Decoder.decodeToWav(src, dst);
+                    } catch (Exception e) {
+                        return;
+                    }
+                } else {
+                    Files.copy(src, dst);
+                }
+            }
+
+            String name = soundFile.replaceAll("(?i)\\.\\w+$", "");
             Path soundsJson = assetDir.resolve("assets/justasplash/sounds.json");
             if (!Files.exists(soundsJson)) {
                 String json = "{\"splash\":{\"sounds\":[{\"name\":\"justasplash:"

src/main/java/net/anomaly/justasplash/util/Mp3Decoder.java

@@ -0,0 +1,92 @@
+package net.anomaly.justasplash.util;
+
+import javazoom.jl.decoder.Bitstream;
+import javazoom.jl.decoder.Decoder;
+import javazoom.jl.decoder.Header;
+import javazoom.jl.decoder.SampleBuffer;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+public class Mp3Decoder {
+    public static void decodeToWav(Path mp3Path, Path wavPath) throws Exception {
+        byte[] pcmData;
+        int sampleRate = 44100;
+        int channels = 2;
+
+        try (InputStream input = Files.newInputStream(mp3Path)) {
+            Bitstream bitstream = new Bitstream(input);
+            Decoder decoder = new Decoder();
+            ByteArrayOutputStream pcmOut = new ByteArrayOutputStream();
+
+            boolean first = true;
+            while (true) {
+                Header header = bitstream.readFrame();
+                if (header == null) break;
+
+                SampleBuffer output = (SampleBuffer) decoder.decodeFrame(header, bitstream);
+                if (first) {
+                    sampleRate = decoder.getOutputFrequency();
+                    channels = decoder.getOutputChannels();
+                    first = false;
+                }
+
+                short[] samples = output.getBuffer();
+                int len = output.getBufferLength();
+                byte[] bytes = new byte[len * 2];
+                for (int i = 0; i < len; i++) {
+                    bytes[i * 2] = (byte) (samples[i] & 0xFF);
+                    bytes[i * 2 + 1] = (byte) ((samples[i] >> 8) & 0xFF);
+                }
+                pcmOut.write(bytes);
+
+                bitstream.closeFrame();
+            }
+
+            pcmData = pcmOut.toByteArray();
+        }
+
+        writeWav(pcmData, sampleRate, channels, 16, wavPath);
+    }
+
+    private static void writeWav(byte[] pcmData, int sampleRate, int channels, int bitsPerSample, Path output) throws IOException {
+        int byteRate = sampleRate * channels * bitsPerSample / 8;
+        int blockAlign = channels * bitsPerSample / 8;
+        int dataSize = pcmData.length;
+
+        try (DataOutputStream dos = new DataOutputStream(Files.newOutputStream(output))) {
+            dos.writeBytes("RIFF");
+            writeLEInt(dos, 36 + dataSize);
+            dos.writeBytes("WAVE");
+
+            dos.writeBytes("fmt ");
+            writeLEInt(dos, 16);
+            writeLEShort(dos, (short) 1);
+            writeLEShort(dos, (short) channels);
+            writeLEInt(dos, sampleRate);
+            writeLEInt(dos, byteRate);
+            writeLEShort(dos, (short) blockAlign);
+            writeLEShort(dos, (short) bitsPerSample);
+
+            dos.writeBytes("data");
+            writeLEInt(dos, dataSize);
+            dos.write(pcmData);
+        }
+    }
+
+    private static void writeLEInt(DataOutputStream dos, int value) throws IOException {
+        dos.writeByte(value & 0xFF);
+        dos.writeByte((value >> 8) & 0xFF);
+        dos.writeByte((value >> 16) & 0xFF);
+        dos.writeByte((value >> 24) & 0xFF);
+    }
+
+    private static void writeLEShort(DataOutputStream dos, short value) throws IOException {
+        dos.writeByte(value & 0xFF);
+        dos.writeByte((value >> 8) & 0xFF);
+    }
+}