feat: handle video decode errors with transcode fallback

verify_sync.py

@@ -406,6 +406,9 @@ class VerifyWindow(QtWidgets.QMainWindow):
         # Wait for media loaded to get actual duration
         self.media_player.durationChanged.connect(self._on_duration_changed)
 
+        # Handle video decode errors — transcode and retry
+        self.media_player.errorOccurred.connect(self._on_media_error)
+
     def _on_duration_changed(self, dur_ms):
         """QMediaPlayer reports actual video duration in ms."""
         vid_dur = dur_ms / 1000.0
@@ -424,6 +427,30 @@ class VerifyWindow(QtWidgets.QMainWindow):
             self.btn_play.setText("Play")
             self.audio_player.stop()
 
+    def _on_media_error(self, error, message):
+        """Handle video decode failure — transcode to H.264 and retry."""
+        if getattr(self, "_transcode_attempted", False):
+            print(f"Video error even after transcode: {message}", file=sys.stderr)
+            return
+        print(f"Video decode error ({error.name}): {message}", file=sys.stderr)
+        print("Attempting fallback: transcoding to H.264 SDR...", file=sys.stderr)
+        self._transcode_attempted = True
+
+        if self.temp_dir is None:
+            self.temp_dir = tempfile.mkdtemp(prefix="verify_sync_")
+        preview_path = os.path.join(self.temp_dir, "preview.mp4")
+        transcode_dur = 30.0 if self.mode == "short" else 0
+
+        if not transcode_to_h264_sdr(self.video_path, preview_path, transcode_dur):
+            print("Transcode also failed — video will remain black", file=sys.stderr)
+            return
+
+        # Reload with the transcoded file
+        self.video_path = preview_path
+        from PyQt6.QtCore import QUrl
+        self.media_player.setSource(QUrl.fromLocalFile(os.path.abspath(preview_path)))
+        print(f"Retrying with transcoded preview: {preview_path}")
+
     def _draw_waveforms(self):
         max_pts = 200_000 if self.mode == "full" else 80_000
 
@@ -670,31 +697,6 @@ def main():
     app = QtWidgets.QApplication(sys.argv)
     apply_dark_theme(app)
 
-    # Check if QMediaPlayer supports the video codec; only transcode if needed
-    probe = QtMultimedia.QMediaPlayer()
-    probe.setSource(QtCore.QUrl.fromLocalFile(os.path.abspath(video_path)))
-    support = probe.support()
-    del probe
-
-    if support != QtMultimedia.QMediaPlayer.Support.Supported:
-        if not temp_dir:
-            temp_dir = tempfile.mkdtemp(prefix="verify_sync_")
-        preview_path = os.path.join(temp_dir, "preview.mp4")
-        if not os.path.exists(preview_path):
-            transcode_dur = 30.0 if args.mode == "short" else 0
-            print(f"Codec not supported by QMediaPlayer (support={support.name}), "
-                  f"transcoding to H.264 SDR ({'%.1fs' % transcode_dur if transcode_dur else 'full'})...")
-            if not transcode_to_h264_sdr(video_path, preview_path, transcode_dur):
-                print(f"WARNING: transcode failed, using original video (may show black)", file=sys.stderr)
-            else:
-                video_path = preview_path
-                print(f"Preview ready: {preview_path}")
-        else:
-            video_path = preview_path
-            print(f"Using cached preview: {preview_path}")
-    else:
-        print(f"Codec supported by QMediaPlayer, using directly")
-
     w = VerifyWindow(video_path, wav_a, wav_b, sr=sr, lag_sec=lag_sec,
                      mode=args.mode, out_dir=out_dir, temp_dir=temp_dir,
                      volume=volume)