diff --git a/cht/stream/ffmpeg.py b/cht/stream/ffmpeg.py
index 4110cc5..a7c7f90 100644
--- a/cht/stream/ffmpeg.py
+++ b/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)
diff --git a/cht/stream/manager.py b/cht/stream/manager.py
index 620f303..1952e8b 100644
--- a/cht/stream/manager.py
+++ b/cht/stream/manager.py
@@ -10,10 +10,8 @@ Architecture:
 
 import json
 import logging
-import os
 import re
 import time
-from queue import Queue, Empty
 from threading import Thread
 
 from cht.config import (
@@ -244,10 +242,9 @@ class StreamManager:
         - stderr: parses showinfo lines, queues pts_time values
         - stdout: reads JPEG frames from pipe, pairs with queued timestamps,
           writes files to disk, fires callbacks immediately
-
-        showinfo fires before the JPEG encoder, so timestamps are always
-        queued before the corresponding JPEG data arrives on stdout.
         """
+        from queue import Queue, Empty
+        import os
         ts_queue = Queue()
 
         def _read_stderr():
@@ -269,13 +266,10 @@ class StreamManager:
             buf = b""
             raw_fd = proc.stdout.fileno()
             while True:
-                # os.read on the raw fd returns as soon as ANY data is available
-                # (no Python buffered-IO blocking waiting to fill a buffer)
                 chunk = os.read(raw_fd, 65536)
                 if not chunk:
                     break
                 buf += chunk
-                # Split JPEG frames by SOI (0xFFD8) and EOI (0xFFD9) markers
                 while True:
                     soi = buf.find(b"\xff\xd8")
                     if soi < 0:
@@ -283,12 +277,11 @@ class StreamManager:
                         break
                     eoi = buf.find(b"\xff\xd9", soi + 2)
                     if eoi < 0:
-                        buf = buf[soi:]  # keep from SOI, need more data
+                        buf = buf[soi:]
                         break
                     jpeg_data = buf[soi:eoi + 2]
                     buf = buf[eoi + 2:]
 
-                    # Get timestamp (showinfo fires before encode, so it's queued)
                     try:
                         pts_time = ts_queue.get(timeout=2.0)
                     except Empty: