one behind duplicated, and the correct

cht/stream/ffmpeg.py

@@ -98,7 +98,15 @@ 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
-    select_expr = f"gt(scene,{scene_threshold})"
+    #
+    # Flush trick: select the scene-change frame AND the next 2 frames.
+    # The pipeline has 2 levels of buffering (encoder + muxer), so we
+    # need 2 flush frames to push the real scene-change frame out.
+    # mod(selected_n,3) prevents chaining: after 2 flushes, selected_n
+    # hits a multiple of 3 and the chain stops.
+    scene_expr = f"gt(scene,{scene_threshold})"
+    flush_expr = "eq(n,prev_selected_n+1)*mod(selected_n,3)"
+    select_expr = f"{scene_expr}+{flush_expr}"
     scene_stream = stream.filter("select", select_expr).filter("showinfo")
     scene_out = ffmpeg.output(
         scene_stream, "pipe:1",

cht/stream/manager.py

@@ -263,6 +263,7 @@ class StreamManager:
         def _read_stdout():
             frame_num = start_number
             offset = self.current_global_offset
+            last_pts = -1.0
             buf = b""
             raw_fd = proc.stdout.fileno()
             while True:
@@ -288,6 +289,12 @@ class StreamManager:
                         log.warning("No timestamp for scene frame %d", frame_num)
                         pts_time = 0.0
 
+                    # Skip flush frames (within 100ms of previous = duplicate)
+                    if pts_time - last_pts < 0.1:
+                        log.debug("Skipping flush frame at pts=%.3f", pts_time)
+                        continue
+                    last_pts = pts_time
+
                     frame_id = f"F{frame_num:04d}"
                     frame_path = self.frames_dir / f"{frame_id}.jpg"
                     frame_path.write_bytes(jpeg_data)