fix: HLS audio via KVO+polling for playerItem.tracks, diagnostic logging

- KVO观察playerItem.tracks变化(HLS tracks异步加载)
- 轮询保底(20秒超时)，KVO不触发时仍能捕获
- 诊断日志：打印每个track的mediaType/trackID
- tap回调改进：始终先GetSourceAudio保证管道不阻塞
- 窗口标题随toolbar联动

Sources/PlayerRecorder.swift

@@ -184,6 +184,7 @@ final class PlayerRecorder: NSObject {
     private var audioTap: MTAudioProcessingTap?
     private var audioContext: AudioCaptureContext?
     private weak var currentPlayerItem: AVPlayerItem?
+    private var tracksObservation: NSKeyValueObservation?
     
     // 录制起始时间（用于计算视频相对时间戳）
     nonisolated(unsafe) private var recordStartTime: CMTime = .zero
@@ -292,6 +293,7 @@ final class PlayerRecorder: NSObject {
         
         // 停止音频 tap
         audioContext?.isRunning = false
+        tracksObservation = nil
         let totalAudioFrames = audioContext?.appendCount ?? 0
         let processCalls = audioContext?.processCallCount ?? 0
         NSLog("[Recorder] Stopping: videoFrames=%d, audioProcessCalls=%d, audioAppended=%d",
@@ -336,52 +338,74 @@ final class PlayerRecorder: NSObject {
     // MARK: - 音频 Tap 设置
     
     private func setupAudioTap(playerItem: AVPlayerItem, audioWriterInput: AVAssetWriterInput) {
-        // 两步策略查找音频 track：
-        // 1) playerItem.tracks（已加载的 track，trackID 与 audioMix 匹配）
-        // 2) asset.loadTracks（fallback，HLS 可能 tracks 尚未填充）
+        // HLS 流的 tracks 是异步加载的
+        // 策略：先同步检查 → KVO 观察 → 定时轮询保底
         
+        // 先尝试直接获取（本地文件场景）
+        if let audioTrack = self.findAudioTrackID(in: playerItem) {
+            NSLog("[Recorder] ✓ Audio track immediately available: trackID=%d", audioTrack)
+            self.installTap(on: playerItem, trackID: audioTrack, audioWriterInput: audioWriterInput)
+            return
+        }
+        
+        // tracks 尚未加载 — 用 KVO 观察变化
+        NSLog("[Recorder] ⏳ Audio tracks not yet loaded, setting up KVO + polling...")
+        
+        let observation = playerItem.observe(\.tracks, options: [.new]) { [weak self] item, _ in
+            guard let self, self.isRunning, self.audioTap == nil else { return }
+            
+            if let trackID = self.findAudioTrackID(in: item) {
+                NSLog("[Recorder] ✓ Audio track via KVO: trackID=%d", trackID)
+                Task { @MainActor in
+                    guard self.isRunning, self.audioTap == nil else { return }
+                    self.installTap(on: item, trackID: trackID, audioWriterInput: audioWriterInput)
+                }
+                self.tracksObservation = nil
+            }
+        }
+        self.tracksObservation = observation
+        
+        // 保底：在视频抓帧循环中定期检查（HLS KVO 可能不触发）
+        // 超时保护：20秒后放弃
         Task {
             var attempts = 0
+            while attempts < 200 && self.isRunning && self.audioTap == nil { // 20秒
+                try await Task.sleep(nanoseconds: 100_000_000) // 0.1秒
+                attempts += 1
                 
-            // 阶段1：尝试 playerItem.tracks（最多 3 秒）
-            while attempts < 30 {
-                guard self.isRunning else { return }
-                
-                let itemTracks = playerItem.tracks
-                if let audioItemTrack = itemTracks.first(where: { $0.assetTrack?.mediaType == .audio }),
-                   let assetTrack = audioItemTrack.assetTrack {
-                    let trackID = assetTrack.trackID
-                    NSLog("[Recorder] ✓ Audio track via playerItem.tracks: trackID=%d", trackID)
-                    self.installTap(on: playerItem, trackID: trackID, audioWriterInput: audioWriterInput)
+                if let trackID = self.findAudioTrackID(in: playerItem) {
+                    NSLog("[Recorder] ✓ Audio track via polling (attempt %d): trackID=%d", attempts, trackID)
+                    await MainActor.run {
+                        guard self.isRunning, self.audioTap == nil else { return }
+                        self.installTap(on: playerItem, trackID: trackID, audioWriterInput: audioWriterInput)
+                    }
+                    self.tracksObservation = nil
                     return
                 }
-                
-                attempts += 1
-                try await Task.sleep(nanoseconds: 100_000_000) // 0.1秒
             }
-            
-            // 阶段2：fallback — asset.loadTracks（最多再等 5 秒）
-            NSLog("[Recorder] ⚠️ playerItem.tracks empty, falling back to asset.loadTracks")
-            attempts = 0
-            while attempts < 50 {
-                guard self.isRunning else { return }
-                
-                if let assetTracks = try? await playerItem.asset.loadTracks(withMediaType: .audio),
-                   let audioTrack = assetTracks.first {
-                    let trackID = audioTrack.trackID
-                    NSLog("[Recorder] ✓ Audio track via asset.loadTracks: trackID=%d", trackID)
-                    self.installTap(on: playerItem, trackID: trackID, audioWriterInput: audioWriterInput)
-                    return
-                }
-                
-                attempts += 1
-                try await Task.sleep(nanoseconds: 100_000_000) // 0.1秒
+            if self.audioTap == nil {
+                NSLog("[Recorder] ❌ No audio track found after %d polling attempts", attempts)
+                self.tracksObservation = nil
             }
-            
-            NSLog("[Recorder] ❌ No audio track found after both attempts")
         }
     }
     
+    /// 从 playerItem.tracks 查找音频 trackID
+    private func findAudioTrackID(in playerItem: AVPlayerItem) -> CMPersistentTrackID? {
+        let itemTracks = playerItem.tracks
+        guard !itemTracks.isEmpty else { return nil }
+        
+        for (i, track) in itemTracks.enumerated() {
+            guard let assetTrack = track.assetTrack else { continue }
+            NSLog("[Recorder]   track[%d]: mediaType=%@, trackID=%d, isEnabled=%d",
+                  i, assetTrack.mediaType.rawValue as NSString, assetTrack.trackID, track.isEnabled)
+            if assetTrack.mediaType == .audio {
+                return assetTrack.trackID
+            }
+        }
+        return nil
+    }
+    
     private func installTap(on playerItem: AVPlayerItem, trackID: CMPersistentTrackID, audioWriterInput: AVAssetWriterInput) {
         // 创建音频捕获上下文
         let context = AudioCaptureContext()