Fix: use Timer for video capture, set isRunning before capture loop

Sources/PlayerRecorder.swift

@@ -88,6 +88,7 @@ final class PlayerRecorder: NSObject {
         
         // 启动视频抓帧
         isRecording = true
+        isRunning = true  // 必须在 startCaptureLoop 之前设置
         startTimer()
         startCaptureLoop()
         
@@ -100,6 +101,8 @@ final class PlayerRecorder: NSObject {
         guard isRecording else { return }
         isRecording = false
         isRunning = false
+        captureTimer?.invalidate()
+        captureTimer = nil
         stopTimer()
         stopAudioCapture()
         
@@ -117,13 +120,13 @@ final class PlayerRecorder: NSObject {
     }
     
     // MARK: - 视频抓帧
+    private var captureTimer: Timer?
+    
     private func startCaptureLoop() {
-        guard let vInput = videoInput else { return }
-        let queue = DispatchQueue(label: "recorder.video.capture")
-        vInput.requestMediaDataWhenReady(on: queue) { [weak self] in
-            guard let self = self, self.isRunning else { return }
+        // 用 Timer 每 1/30 秒抓一帧
+        captureTimer = Timer.scheduledTimer(withTimeInterval: 1.0 / 30.0, repeats: true) { [weak self] _ in
             Task { @MainActor in
-                self.captureVideoFrame()
+                self?.captureVideoFrame()
             }
         }
     }