mdfpwm support

mdfpwmWriter.ts

@@ -0,0 +1,49 @@
+export interface MDFPWMMetadata {
+  title?: string;
+  artist?: string;
+  album?: string;
+}
+
+function toS1(str: string): Buffer {
+  const utf8 = Buffer.from(str, "utf-8");
+  const len = utf8.length;
+  return Buffer.concat([Buffer.from([len]), utf8]);
+}
+
+export function writeMDFPWMv3(
+  left: Buffer,
+  right: Buffer,
+  meta: MDFPWMMetadata = {}
+): Buffer {
+  if (left.length !== right.length) {
+    throw new Error("Left and right DFPWM buffers must be the same length");
+  }
+
+  let length = left.byteLength*2;
+  const mdfpwm = []
+  mdfpwm.push(Buffer.from("MDFPWM\x03", "ascii"));
+  mdfpwm.push(Buffer.alloc(4));
+  mdfpwm.push(toS1(meta.artist || ""));
+  mdfpwm.push(toS1(meta.title || ""));
+  mdfpwm.push(toS1(meta.album || ""));
+  mdfpwm[1]!.writeUint32LE(length)
+
+  for(let i =0; i < length / 12000; i++) {
+    const lStart = i * 6000;
+    const rStart = i * 6000;
+
+    const lChunk = left.subarray(lStart, lStart + 6000);
+    mdfpwm.push(lChunk);
+    if (lChunk.length < 6000) {
+        mdfpwm.push(Buffer.alloc(6000 - lChunk.length, 0x55));
+    }
+
+    const rChunk = right.subarray(rStart, rStart + 6000);
+    mdfpwm.push(rChunk);
+    if (rChunk.length < 6000) {
+        mdfpwm.push(Buffer.alloc(6000 - rChunk.length, 0x55));
+    }
+  }
+
+  return Buffer.concat(mdfpwm)
+}