consisten one behind

cht/stream/ffmpeg.py

@@ -97,13 +97,13 @@ def receive_record_relay_and_detect(stream_url, output_path, relay_url,
     )
 
     # Scene detection: CUDA decode (GPU) → select filter (CPU, lightweight)
-    # → showinfo → MJPEG piped to stdout (avoids image2 muxer one-frame buffer)
+    # → showinfo → MJPEG piped to stdout
     select_expr = f"gt(scene,{scene_threshold})"
     scene_stream = stream.filter("select", select_expr).filter("showinfo")
     scene_out = ffmpeg.output(
         scene_stream, "pipe:1",
         f="image2pipe", vcodec="mjpeg",
-        vsync="vfr", flush_packets=1, **{"q:v": "2"},
+        flush_packets=1, **{"q:v": "2", "fps_mode": "passthrough"},
     )
 
     return ffmpeg.merge_outputs(file_out, relay_out, scene_out).global_args(*GLOBAL_ARGS)