fix: 改用Web Audio直接采集PCM，解决decodeAudioData失败

MediaRecorder的webm被decodeAudioData解码常失败（尤其短录音）。
改为录音时用ScriptProcessor实时采集原始Float32 PCM，
停止后直接重采样16k编码WAV，完全绕开容器解码。
新增：录音过短(<0.3s)提示、资源清理。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pages/ai-chat/index.vue

@@ -173,33 +173,46 @@ export default {
       sessionId: 'app_' + Date.now(),
       history: [],
       exampleTags: ['各班组查获排名', '打火机查获数量', '旅检一部人员资质', '全站党员人数'],
-      // 录音相关
+      // 录音相关（Web Audio 直接采集 PCM）
       recording: false,
-      mediaRecorder: null,
-      audioChunks: [],
       recordCancelled: false,
+      audioCtx: null,
+      mediaStream: null,
+      sourceNode: null,
+      scriptNode: null,
+      pcmChunks: [],
+      pcmSampleRate: 16000,
     }
   },
   methods: {
-    // ============ 录音相关 ============
+    // ============ 录音相关（Web Audio 直接采集原始 PCM，避免 decodeAudioData 失败）============
     async startRecord(e) {
       if (this.loading) return
       this.recordCancelled = false
-      this.audioChunks = []
+      this.pcmChunks = []
 
       try {
         const stream = await navigator.mediaDevices.getUserMedia({ audio: true })
-        this.mediaRecorder = new MediaRecorder(stream)
-        this.mediaRecorder.ondataavailable = (ev) => {
-          if (ev.data.size > 0) this.audioChunks.push(ev.data)
+        this.mediaStream = stream
+
+        const AudioCtx = window.AudioContext || window.webkitAudioContext
+        const ctx = new AudioCtx()
+        if (ctx.state === 'suspended') await ctx.resume()
+        this.audioCtx = ctx
+        this.pcmSampleRate = ctx.sampleRate
+
+        const source = ctx.createMediaStreamSource(stream)
+        const node = ctx.createScriptProcessor(4096, 1, 1)
+        node.onaudioprocess = (ev) => {
+          if (!this.recording) return
+          // 复制一份当前帧的 Float32 PCM
+          this.pcmChunks.push(new Float32Array(ev.inputBuffer.getChannelData(0)))
         }
-        this.mediaRecorder.onstop = () => {
-          stream.getTracks().forEach(t => t.stop())
-          if (!this.recordCancelled && this.audioChunks.length) {
-            this.submitAudio()
-          }
-        }
-        this.mediaRecorder.start()
+        source.connect(node)
+        node.connect(ctx.destination)
+
+        this.sourceNode = source
+        this.scriptNode = node
         this.recording = true
       } catch (err) {
         let msg = '无法访问麦克风'
@@ -214,36 +227,53 @@ export default {
       }
     },
 
+    _teardownAudio() {
+      try { if (this.scriptNode) { this.scriptNode.disconnect(); this.scriptNode.onaudioprocess = null } } catch (e) {}
+      try { if (this.sourceNode) this.sourceNode.disconnect() } catch (e) {}
+      try { if (this.mediaStream) this.mediaStream.getTracks().forEach(t => t.stop()) } catch (e) {}
+      try { if (this.audioCtx) this.audioCtx.close() } catch (e) {}
+      this.scriptNode = null
+      this.sourceNode = null
+      this.mediaStream = null
+      this.audioCtx = null
+    },
+
     stopRecord(e) {
-      if (!this.recording || !this.mediaRecorder) return
+      if (!this.recording) return
       this.recording = false
-      this.mediaRecorder.stop()
+      const rate = this.pcmSampleRate
+      const chunks = this.pcmChunks
+      this._teardownAudio()
+      if (!this.recordCancelled) this.submitAudio(chunks, rate)
     },
 
     cancelRecord(e) {
-      if (!this.recording || !this.mediaRecorder) return
+      if (!this.recording) return
       this.recordCancelled = true
       this.recording = false
-      this.mediaRecorder.stop()
+      this._teardownAudio()
     },
 
-    // 鼠标移出按钮：录音中则发送（等同松手），未录音则忽略
+    // 鼠标移出按钮：录音中则发送（等同松手）
     onMicLeave(e) {
-      if (this.recording && this.mediaRecorder) {
-        this.recording = false
-        this.mediaRecorder.stop()
-      }
+      if (this.recording) this.stopRecord(e)
     },
 
-    async submitAudio() {
-      const mimeType = (this.audioChunks[0] && this.audioChunks[0].type) || 'audio/webm'
-      const srcBlob = new Blob(this.audioChunks, { type: mimeType })
+    async submitAudio(chunks, srcRate) {
+      // 合并所有 PCM 帧
+      let total = 0
+      for (const c of chunks) total += c.length
+      if (total < srcRate * 0.3) {  // 少于0.3秒视为无效
+        uni.showToast({ title: '录音太短，请长按说话', icon: 'none' })
+        return
+      }
+      const merged = new Float32Array(total)
+      let pos = 0
+      for (const c of chunks) { merged.set(c, pos); pos += c.length }
 
       uni.showLoading({ title: '识别中...' })
       try {
-        // 浏览器端转成百度要求的 16k 单声道 16bit WAV
-        const wavBlob = await this.encodeWav16k(srcBlob)
-
+        const wavBlob = this.encodeWav16k(merged, srcRate)
         const formData = new FormData()
         formData.append('file', wavBlob, 'voice.wav')
 
@@ -262,39 +292,21 @@ export default {
       }
     },
 
-    // 把任意录音 Blob 解码 → 混单声道 → 重采样16k → 编码16bit PCM WAV
-    async encodeWav16k(blob) {
-      const arrayBuffer = await blob.arrayBuffer()
-      const AudioCtx = window.AudioContext || window.webkitAudioContext
-      const ctx = new AudioCtx()
-      const decoded = await ctx.decodeAudioData(arrayBuffer)
-      ctx.close()
-
-      // 混成单声道
-      const numCh = decoded.numberOfChannels
-      const srcLen = decoded.length
-      const mono = new Float32Array(srcLen)
-      for (let ch = 0; ch < numCh; ch++) {
-        const ch_data = decoded.getChannelData(ch)
-        for (let i = 0; i < srcLen; i++) mono[i] += ch_data[i] / numCh
-      }
-
-      // 线性插值重采样到 16000
+    // Float32 PCM → 混（已单声道）→ 重采样16k → 16bit PCM WAV
+    encodeWav16k(mono, srcRate) {
       const dstRate = 16000
-      const srcRate = decoded.sampleRate
-      const dstLen = Math.round(srcLen * dstRate / srcRate)
+      const dstLen = Math.round(mono.length * dstRate / srcRate)
       const out = new Float32Array(dstLen)
       const ratio = srcRate / dstRate
       for (let i = 0; i < dstLen; i++) {
-        const pos = i * ratio
-        const idx = Math.floor(pos)
-        const frac = pos - idx
+        const p = i * ratio
+        const idx = Math.floor(p)
+        const frac = p - idx
         const s0 = mono[idx] || 0
-        const s1 = mono[idx + 1] || s0
+        const s1 = mono[idx + 1] !== undefined ? mono[idx + 1] : s0
         out[i] = s0 + (s1 - s0) * frac
       }
 
-      // 编码 WAV (44字节头 + 16bit PCM)
       const buffer = new ArrayBuffer(44 + dstLen * 2)
       const view = new DataView(buffer)
       const writeStr = (off, str) => { for (let i = 0; i < str.length; i++) view.setUint8(off + i, str.charCodeAt(i)) }
@@ -303,8 +315,8 @@ export default {
       writeStr(8, 'WAVE')
       writeStr(12, 'fmt ')
       view.setUint32(16, 16, true)
-      view.setUint16(20, 1, true)        // PCM
-      view.setUint16(22, 1, true)        // 单声道
+      view.setUint16(20, 1, true)
+      view.setUint16(22, 1, true)
       view.setUint32(24, dstRate, true)
       view.setUint32(28, dstRate * 2, true)
       view.setUint16(32, 2, true)
@@ -313,7 +325,7 @@ export default {
       view.setUint32(40, dstLen * 2, true)
       let off = 44
       for (let i = 0; i < dstLen; i++) {
-        let s = Math.max(-1, Math.min(1, out[i]))
+        const s = Math.max(-1, Math.min(1, out[i]))
         view.setInt16(off, s < 0 ? s * 0x8000 : s * 0x7FFF, true)
         off += 2
       }