静音与停止发布

const mic = srtc.createLocalMicTrack(micPresetMusic());
await mic.startCapture();
await channel.publishLocalAudioTrack(mic);

mic.mute();      // 关麦
mic.unmute();    // 开麦

// 关摄像头
await channel.unpublishLocalVideoTrack(camera);
await camera.stopCapture();

// 重新开：要重新创建轨道
const camera2 = srtc.createLocalCameraTrack(cameraPreset720p());
await camera2.startCapture();
await channel.publishLocalVideoTrack(camera2);

const camera = srtc.createLocalCameraTrack(cameraPreset720p());
await camera.startCapture();   // 到这里本地预览已经能显示了
// 不调 publishLocalVideoTrack

// ❌ 错的：轨道换了底层 source，但发布关系还指着旧的
await mic.changeDeviceId(newDeviceId);

// ✅ 对的
await channel.unpublishLocalAudioTrack(mic);
await mic.changeDeviceId(newDeviceId);
await channel.publishLocalAudioTrack(mic);

// 只停本地播放，仍在订阅（带宽照旧消耗，切回来是瞬时的）
channel.setUserAudioPlayback(uid, false);
channel.setRemoteAudioPlayback(false);          // 全体

// 真正退订（省带宽，但恢复要重新协商）
await channel.unsubscribeRemoteTrack(track, 0);