fix: improve HLS audio track discovery - async load fallback + detailed diagnostics

- setupAudioTap: log all tracks at start, KVO count changes
- findAudioTrackID: log when assetTrack is nil (HLS not loaded)
- Polling: add async asset.load(.tracks) fallback after 5s
- Extend timeout from 20s to 30s
- Status log every 5s during polling

Sources/PlayerRecorder.swift

@@ -339,7 +339,19 @@ final class PlayerRecorder: NSObject {
     
     private func setupAudioTap(playerItem: AVPlayerItem, audioWriterInput: AVAssetWriterInput) {
         // 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
+        // 策略：先同步检查 → KVO 观察 → 定时轮询保底（含 async load 备选）
+        
+        // 先打印当前 track 状态（诊断）
+        let tracks = playerItem.tracks
+        NSLog("[Recorder] setupAudioTap: playerItem.tracks.count=%d", tracks.count)
+        for (i, track) in tracks.enumerated() {
+            if let at = track.assetTrack {
+                NSLog("[Recorder]   track[%d]: mediaType=%@, trackID=%d, enabled=%d",
+                      i, at.mediaType.rawValue as NSString, at.trackID, track.isEnabled)
+            } else {
+                NSLog("[Recorder]   track[%d]: assetTrack=NIL (HLS not loaded yet?)", i)
+            }
+        }
         
         // 先尝试直接获取（本地文件场景）
         if let audioTrack = self.findAudioTrackID(in: playerItem) {
@@ -354,6 +366,9 @@ final class PlayerRecorder: NSObject {
         let observation = playerItem.observe(\.tracks, options: [.new]) { [weak self] item, _ in
             guard let self, self.isRunning, self.audioTap == nil else { return }
             
+            let tCount = item.tracks.count
+            NSLog("[Recorder] KVO tracks changed: count=%d", tCount)
+            
             if let trackID = self.findAudioTrackID(in: item) {
                 NSLog("[Recorder] ✓ Audio track via KVO: trackID=%d", trackID)
                 Task { @MainActor in
@@ -365,14 +380,16 @@ final class PlayerRecorder: NSObject {
         }
         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
+        // 保底轮询：含 async asset.load(.tracks) 备选
+        // 超时保护：30秒后放弃
         Task {
             var attempts = 0
-            while attempts < 200 && self.isRunning && self.audioTap == nil { // 20秒
+            var didTryAsyncLoad = false
+            while attempts < 300 && self.isRunning && self.audioTap == nil { // 30秒
                 try await Task.sleep(nanoseconds: 100_000_000) // 0.1秒
                 attempts += 1
                 
+                // 方式1: 从 playerItem.tracks 查找
                 if let trackID = self.findAudioTrackID(in: playerItem) {
                     NSLog("[Recorder] ✓ Audio track via polling (attempt %d): trackID=%d", attempts, trackID)
                     await MainActor.run {
@@ -382,22 +399,59 @@ final class PlayerRecorder: NSObject {
                     self.tracksObservation = nil
                     return
                 }
+                
+                // 方式2: 5秒后尝试 async load asset tracks（HLS 可能通过这个路径加载）
+                if !didTryAsyncLoad && attempts >= 50 {
+                    didTryAsyncLoad = true
+                    NSLog("[Recorder] Trying async asset.load(.tracks)...")
+                    do {
+                        let assetTracks = try await playerItem.asset.load(.tracks)
+                        NSLog("[Recorder] async load returned %d tracks", assetTracks.count)
+                        for (i, t) in assetTracks.enumerated() {
+                            NSLog("[Recorder]   assetTrack[%d]: mediaType=%@, trackID=%d",
+                                  i, t.mediaType.rawValue as NSString, t.trackID)
+                        }
+                        if let audioAssetTrack = assetTracks.first(where: { $0.mediaType == .audio }) {
+                            let trackID = audioAssetTrack.trackID
+                            NSLog("[Recorder] ✓ Audio track via async load: trackID=%d", trackID)
+                            await MainActor.run {
+                                guard self.isRunning, self.audioTap == nil else { return }
+                                self.installTap(on: playerItem, trackID: trackID, audioWriterInput: audioWriterInput)
+                            }
+                            self.tracksObservation = nil
+                            return
+                        }
+                    } catch {
+                        NSLog("[Recorder] async load failed: %@", error.localizedDescription)
+                    }
+                }
+                
+                // 每5秒打一次状态日志
+                if attempts % 50 == 0 {
+                    let tc = playerItem.tracks.count
+                    NSLog("[Recorder] polling attempt %d: playerItem.tracks.count=%d, tapInstalled=%d",
+                          attempts, tc, self.audioTap != nil ? 1 : 0)
+                }
             }
             if self.audioTap == nil {
-                NSLog("[Recorder] ❌ No audio track found after %d polling attempts", attempts)
+                NSLog("[Recorder] ❌ No audio track found after %d polling attempts (30s timeout)", attempts)
                 self.tracksObservation = nil
             }
         }
     }
     
     /// 从 playerItem.tracks 查找音频 trackID
+    /// 对 HLS 流，assetTrack 可能延迟加载或始终为 nil
     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",
+            guard let assetTrack = track.assetTrack else {
+                NSLog("[Recorder]   findTrack: track[%d] assetTrack=nil (not loaded)", i)
+                continue
+            }
+            NSLog("[Recorder]   findTrack: track[%d] mediaType=%@, trackID=%d, enabled=%d",
                   i, assetTrack.mediaType.rawValue as NSString, assetTrack.trackID, track.isEnabled)
             if assetTrack.mediaType == .audio {
                 return assetTrack.trackID