first try new approach

cht/stream/ffmpeg.py

@@ -39,7 +39,7 @@ def receive_and_record(stream_url, output_path):
     )
 
 
-def receive_record_and_relay(stream_url, output_path, relay_url, scene_relay_url=None):
+def receive_record_and_relay(stream_url, output_path, relay_url):
     """Receive TCP stream, write to fragmented MP4, and relay to UDP loopback.
 
     Fragmented MP4 (frag_keyframe+empty_moov) avoids MKV tail corruption:
@@ -47,7 +47,6 @@ def receive_record_and_relay(stream_url, output_path, relay_url, scene_relay_url
     always valid up to the last complete fragment (~1 keyframe interval ≈ 2s).
 
     Uses ffmpeg tee via merge_outputs: one process, identical timestamps.
-    Optionally sends a second relay for the scene detector.
     """
     stream = ffmpeg.input(stream_url, fflags="nobuffer", flags="low_delay")
     file_out = ffmpeg.output(
@@ -61,50 +60,49 @@ def receive_record_and_relay(stream_url, output_path, relay_url, scene_relay_url
         stream, relay_url,
         c="copy", f="mpegts",
     )
-    outputs = [file_out, relay_out]
-    if scene_relay_url:
-        scene_out = ffmpeg.output(
-            stream, scene_relay_url,
-            c="copy", f="mpegts",
-        )
-        outputs.append(scene_out)
-    return ffmpeg.merge_outputs(*outputs).global_args(*QUIET_ARGS)
+    return ffmpeg.merge_outputs(file_out, relay_out).global_args(*QUIET_ARGS)
 
 
-def start_live_scene_detector(stream_url, output_dir, scene_threshold=0.10,
-                              start_number=1):
-    """Start a persistent ffmpeg process that detects scenes from a live stream.
+def receive_record_relay_and_detect(stream_url, output_path, relay_url,
+                                    frames_dir, scene_threshold=0.10,
+                                    start_number=1):
+    """Single process: receive TCP → record fMP4 + relay UDP + scene detect.
 
-    Reads from the UDP relay in real-time — no file seeking, no restart overhead.
-    Writes frame JPEGs and emits showinfo on stderr as scenes are detected.
-    Returns the async process (stderr must be read continuously).
+    One ffmpeg process, three output branches from the same TCP input:
+    1. File output — c=copy to fMP4
+    2. UDP relay — c=copy to mpegts for live display
+    3. Scene frames — CUDA decode → select(scene) → showinfo → JPEG files
+
+    The scene filter runs on decoded frames in-process, so detection latency
+    is near-zero (no polling, no file re-reading, no separate process).
+    Stderr must be read continuously to parse showinfo lines.
     """
+    stream = ffmpeg.input(stream_url, fflags="nobuffer", flags="low_delay",
+                          hwaccel="cuda")
+
+    # Copy outputs (raw packet remux, no decode)
+    file_out = ffmpeg.output(
+        stream, str(output_path),
+        c="copy", f="mp4",
+        movflags="frag_keyframe+empty_moov+default_base_moof",
+        flush_packets=1,
+        **{"bsf:a": "aac_adtstoasc"},
+    )
+    relay_out = ffmpeg.output(
+        stream, relay_url,
+        c="copy", f="mpegts",
+    )
+
+    # Scene detection output (decode + filter → JPEG)
     select_expr = f"gt(scene,{scene_threshold})"
-
-    stream = ffmpeg.input(
-        stream_url,
-        fflags="nobuffer+flush_packets",
-        flags="low_delay",
-        probesize="32000",
-        analyzeduration="0",
-        hwaccel="cuda",
-    )
-    stream = stream.filter("select", select_expr).filter("showinfo")
-
-    output = (
-        ffmpeg.output(
-            stream,
-            str(output_dir / "F%04d.jpg"),
-            vsync="vfr",
-            flush_packets=1,
-            **{"q:v": "2"},
-            start_number=start_number,
-        )
-        .global_args(*GLOBAL_ARGS)
+    scene_stream = stream.filter("select", select_expr).filter("showinfo")
+    scene_out = ffmpeg.output(
+        scene_stream, str(frames_dir / "F%04d.jpg"),
+        vsync="vfr", flush_packets=1, **{"q:v": "2"},
+        start_number=start_number,
     )
 
-    log.info("start_live_scene_detector: %s", " ".join(output.compile()))
-    return run_async(output, pipe_stderr=True)
+    return ffmpeg.merge_outputs(file_out, relay_out, scene_out).global_args(*GLOBAL_ARGS)
 
 
 def extract_scene_frames(input_path, output_dir, scene_threshold=0.10,