fix: 增加双声道合并为单声道的实现

src/index.tsx

@@ -461,27 +461,47 @@ export function Home() {
     Logger.info('jensen', 'bluetooth', 'Clear Paired Devices: ' + JSON.stringify(rst));
   }
 
-  const rms = (u8: Uint8Array) => {
+  /**
+   * 计算双声道PCM数据的RMS和单声道PCM数据
+   * @param u8 - 双声道PCM数据
+   * @returns - 左声道RMS，右声道RMS，单声道PCM数据
+   */
+  const rms = (u8: Uint8Array): [number, number, Int8Array] => {
+    if (!u8 || u8.byteLength <= 8) return [0, 0, new Int8Array(0)];
+    const frameCount = Math.floor((u8.length - 8) / 4); // 每帧: L(2B)+R(2B)
+    if (frameCount <= 0) return [0, 0, new Int8Array(0)];
     let sumL = 0;
     let sumR = 0;
-    const frameCount = (u8.length - 8) / 4;
-    for (let i = 8; i < u8.length; i+=4) {
+    const mono8 = new Int8Array(frameCount);
+    let j = 0;
+    for (let i = 8; i + 3 < u8.length; i += 4, j++) {
       const a = u8[i + 0] & 0xff;
       const b = u8[i + 1] & 0xff;
       const c = u8[i + 2] & 0xff;
       const d = u8[i + 3] & 0xff;
-      let l = (b << 8 | a) & 0xffff;
-      let r = (d << 8 | c) & 0xffff;
-      if (l & 0x8000) l = (l & 0x7fff) - 0x8000;
-      if (r & 0x8000) r = (r & 0x7fff) - 0x8000;
-      // console.log('live, l', l, 'r', r);
+      // 小端 16-bit
+      let l = (b << 8) | a;
+      let r = (d << 8) | c;
+      // 还原为有符号 16-bit
+      if (l & 0x8000) l = l - 0x10000;
+      if (r & 0x8000) r = r - 0x10000;
       const nl = l / 32768;
       const nr = r / 32768;
       sumL += nl * nl;
       sumR += nr * nr;
+      // 双声道合成为单声道（16-bit），再压缩为 Int8
+      // C = A + B - (A * B / 32767)
+      let m = l + r - Math.floor((l * r) / 32767);
+      if (m > 32767) m = 32767;
+      else if (m < -32768) m = -32768;
+      let m8 = m >> 8; // 16-bit 转 8-bit（有符号算术右移）
+      if (m8 > 127) m8 = 127;
+      else if (m8 < -128) m8 = -128;
+      mono8[j] = m8;
     }
-    // console.log('live, sumL', sumL, 'sumR', sumR);
-    return [Math.sqrt(sumL / frameCount), Math.sqrt(sumR / frameCount)];
+    const leftRms = Math.sqrt(sumL / frameCount);
+    const rightRms = Math.sqrt(sumR / frameCount);
+    return [leftRms, rightRms, mono8];
   }
 
   const blocksRef = useRef<Uint8Array[]>([]);
@@ -493,6 +513,7 @@ export function Home() {
     if (live?.data == null) return;
     setLiveStates('live: ' + live.data.length + ' rest: ' + live.rest + ' muted: ' + live.muted);
     // 仅计算，不保留引用；如需录音导出再使用 blocksRef.current.push(live.data.slice(8))
+    blocksRef.current.push(live.data.slice(8));
     const [rms1, rms2] = rms(live.data);
     // console.log('live, rms1', rms1, 'rms2', rms2);
     setRmsLeft(Math.floor(rms1 * 4 * 400));
@@ -525,6 +546,45 @@ export function Home() {
     }
     console.log('live stopped');
     // 将blocks拼接成一个Uint8Array，并下载到本地
+    // 将blocksRef.current的双声道PCM合并为单声道
+    // 每个块都是(interleaved) 2通道，每个通道16bit(2字节)，小端
+    // 合并算法: C = A + B - (A * B / 32767)
+    let monoChunks: Int16Array[] = [];
+    for (const block of blocksRef.current) {
+      // 每帧4字节: L(2字节) R(2字节)
+      let view = new DataView(block.buffer, block.byteOffset, block.byteLength);
+      let sampleCount = block.length / 4;
+      let mono = new Int16Array(sampleCount);
+      for (let i = 0; i < sampleCount; ++i) {
+        let offset = i * 4;
+        let l = view.getInt16(offset, true);
+        let r = view.getInt16(offset + 2, true);
+        // C = A + B - (A * B / 32767)
+        let c = l + r - Math.floor((l * r) / 32767);
+        // 限定在16bit
+        if (c > 32767) c = 32767;
+        if (c < -32768) c = -32768;
+        mono[i] = c;
+      }
+      monoChunks.push(mono);
+    }
+    // 合并所有Int16Array为单一Int16Array
+    const totalSamples = monoChunks.reduce((sum, arr) => sum + arr.length, 0);
+    const monoAll = new Int16Array(totalSamples);
+    let offsetMono = 0;
+    for (const arr of monoChunks) {
+      monoAll.set(arr, offsetMono);
+      offsetMono += arr.length;
+    }
+    // e.g. 可导出为 .pcm 文件
+    let monoBlob = new Blob([monoAll.buffer], { type: 'audio/pcm' });
+    let monoUrl = URL.createObjectURL(monoBlob);
+    let monoA = document.createElement('a');
+    monoA.href = monoUrl;
+    monoA.download = 'live_mono.pcm';
+    monoA.click();
+    URL.revokeObjectURL(monoUrl);
+    /*
     const totalLen = blocksRef.current.reduce((sum, b) => sum + b.length, 0);
     const data = new Uint8Array(totalLen);
     let offset = 0;
@@ -533,7 +593,6 @@ export function Home() {
       offset += b.length;
     }
     // 清空缓存
-    /*
     blocksRef.current = [];
     let blob = new Blob([data], { type: 'audio/pcm' });
     let url = URL.createObjectURL(blob);