feat(audio): 添加单声道转立体声转换功能

- 新增 monoToStereoReader 将单声道 WAV 实时转换为立体声
- PlayWav 自动检测单声道并应用转换管线
- 添加完整的单元测试覆盖转换逻辑
- 整理 import 顺序（goimports）

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

pkg/audio/play.go

@@ -7,11 +7,51 @@ import (
 	"io"
 	"time"
 
-	"github.com/youpy/go-wav"
 	"github.com/hajimehoshi/go-mp3"
+	"github.com/youpy/go-wav"
 	"go.uber.org/zap"
 )
 
+// monoToStereoReader 将单声道音频转换为立体声
+type monoToStereoReader struct {
+	src io.Reader
+	buf []byte
+}
+
+func (m *monoToStereoReader) Read(p []byte) (int, error) {
+	maxSamples := len(p) / 4
+	if maxSamples == 0 {
+		return 0, nil
+	}
+
+	// 按需分配缓冲区
+	if cap(m.buf) < maxSamples*2 {
+		m.buf = make([]byte, maxSamples*2)
+	}
+
+	// 读取单声道数据
+	n, err := m.src.Read(m.buf[:maxSamples*2])
+	if n == 0 {
+		return 0, err
+	}
+
+	// 单声道→立体声：复制每个样本到左右声道
+	samples := n / 2
+	for i := range samples {
+		base := i * 4
+		mono := i * 2
+		p[base] = m.buf[mono]     // 左声道低字节
+		p[base+1] = m.buf[mono+1] // 左声道高字节
+		p[base+2] = m.buf[mono]   // 右声道低字节
+		p[base+3] = m.buf[mono+1] // 右声道高字节
+	}
+
+	if err == io.EOF {
+		return samples * 4, io.EOF
+	}
+	return samples * 4, nil
+}
+
 // PlayWav 播放 WAV 文件(阻塞),直到完成或 context 取消
 func PlayWav(ctx context.Context, r io.ReadCloser) error {
 	// Read the entire file into memory since wav.NewReader needs ReadAt
@@ -33,15 +73,21 @@ func PlayWav(ctx context.Context, r io.ReadCloser) error {
 
 	duration, _ := dec.Duration()
 	sourceRate := int(format.SampleRate)
+	channels := int(format.NumChannels)
 
-	zap.S().Infof("WAV 音频: %d ch, %d Hz, 时长: %v",
-		format.NumChannels, sourceRate, duration)
+	zap.S().Infof("WAV 音频: %d ch, %d Hz, 时长: %v", channels, sourceRate, duration)
+
+	// 构建处理管线：单声道转换 → 重采样
+	reader := io.Reader(dec)
+	if channels == 1 {
+		zap.S().Infof("单声道转立体声: 1 ch → 2 ch")
+		reader = &monoToStereoReader{src: dec}
+		channels = DefaultChannelCount
+	}
 
-	// 需要重采样（使用 Sinc 高质量重采样）
-	var reader io.Reader = dec
 	if needsResampling(sourceRate) {
-		zap.S().Infof("Sinc 重采样: %d Hz → %d Hz", sourceRate, UniversalSampleRate)
-		reader = newSincResampler(dec, sourceRate, UniversalSampleRate, int(format.NumChannels))
+		zap.S().Infof("Sinc 重采样: %d Hz → %d Hz, %d ch", sourceRate, UniversalSampleRate, channels)
+		reader = newSincResampler(reader, sourceRate, UniversalSampleRate, channels)
 	}
 
 	otoCtx, err := initContext()