diff --git a/cht/app.py b/cht/app.py
index 4197405..3807dd8 100644
--- a/cht/app.py
+++ b/cht/app.py
@@ -1,5 +1,7 @@
 import logging
+import os
 import sys
+import threading
 import gi
 
 gi.require_version("Gtk", "4.0")
@@ -25,14 +27,40 @@ class ChtApp(Adw.Application):
         win.present()
 
 
-def _suppress_egl_warnings(domain, level, message, user_data):
-    if b"eglExportDMABUFImage" in message:
-        return
-    GLib.log_default_handler(domain, level, message, user_data)
+_STDERR_SKIP = [b"eglExportDMABUFImage"]
+
+
+def _filter_stderr():
+    """Redirect fd 2 through a pipe; drop lines matching _STDERR_SKIP."""
+    real_stderr_fd = os.dup(2)
+    real_stderr = os.fdopen(real_stderr_fd, "wb", buffering=0)
+    r_fd, w_fd = os.pipe()
+    os.dup2(w_fd, 2)
+    os.close(w_fd)
+
+    def _pump():
+        with os.fdopen(r_fd, "rb", buffering=0) as pipe:
+            buf = b""
+            while True:
+                chunk = pipe.read(4096)
+                if not chunk:
+                    break
+                buf += chunk
+                while b"\n" in buf:
+                    line, buf = buf.split(b"\n", 1)
+                    if line.strip() and not any(skip in line for skip in _STDERR_SKIP):
+                        real_stderr.write(line + b"\n")
+                        real_stderr.flush()
+            if buf:
+                real_stderr.write(buf)
+                real_stderr.flush()
+
+    t = threading.Thread(target=_pump, daemon=True, name="stderr_filter")
+    t.start()
 
 
 def main():
-    GLib.log_set_handler("Gdk", GLib.LogLevelFlags.LEVEL_WARNING, _suppress_egl_warnings, None)
+    _filter_stderr()
     logging.basicConfig(
         level=logging.DEBUG,
         format="%(asctime)s %(levelname)-7s %(name)s: %(message)s",
diff --git a/cht/stream/ffmpeg.py b/cht/stream/ffmpeg.py
index e913c31..ed05133 100644
--- a/cht/stream/ffmpeg.py
+++ b/cht/stream/ffmpeg.py
@@ -40,15 +40,22 @@ def receive_and_record(stream_url, output_path):
 
 
 def receive_record_and_relay(stream_url, output_path, relay_url):
-    """Receive TCP stream, write to MKV, and relay to UDP loopback for live display.
+    """Receive TCP stream, write to fragmented MP4, and relay to UDP loopback.
 
-    Uses ffmpeg tee via merge_outputs: one ffmpeg process handles both outputs
-    from the same decoded input, keeping them in sync with identical timestamps.
+    Fragmented MP4 (frag_keyframe+empty_moov) avoids MKV tail corruption:
+    each keyframe boundary closes a self-contained fragment, so the file is
+    always valid up to the last complete fragment (~1 keyframe interval ≈ 2s).
+    This allows the scene detector to use a 2s safety margin instead of 6s.
+
+    Uses ffmpeg tee via merge_outputs: one process, identical timestamps.
     """
     stream = ffmpeg.input(stream_url, fflags="nobuffer", flags="low_delay")
     file_out = ffmpeg.output(
         stream, str(output_path),
-        c="copy", f="matroska", flush_packets=1,
+        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,
diff --git a/cht/stream/manager.py b/cht/stream/manager.py
index 5090a5c..ac5fd1f 100644
--- a/cht/stream/manager.py
+++ b/cht/stream/manager.py
@@ -56,7 +56,7 @@ class StreamManager:
 
     @property
     def recording_path(self):
-        return self.stream_dir / "recording.mkv"
+        return self.stream_dir / "recording.mp4"
 
     # -- Recording --
 
@@ -81,9 +81,13 @@ class StreamManager:
         def _detect():
             processed_time = 0.0
             frame_count = 0
+            idle_cycles = 0  # consecutive cycles with no new frames
 
             while "stop" not in self._stop_flags:
-                time.sleep(5)
+                # Adaptive sleep: 1s after finding frames, then 2→4→8→10s backoff
+                sleep_secs = 1 if idle_cycles == 0 else min(2, 2 ** idle_cycles)
+                time.sleep(sleep_secs)
+
                 if not self.recording_path.exists():
                     continue
 
@@ -91,16 +95,14 @@ class StreamManager:
                 if size < 100_000:
                     continue
 
-                # Get current duration. Use a 6s safety margin — MKV tail can
-                # be corrupt for several seconds after the last flush, causing
-                # ffmpeg to crash even with a 3s margin.
+                # 2s safety margin — fragmented MP4 is valid up to last complete
+                # keyframe fragment (~1 keyframe interval); 2s covers worst case.
                 safe_duration = self._estimate_safe_duration()
-                if safe_duration is None or safe_duration <= processed_time + 8:
+                if safe_duration is None:
                     continue
 
-                # Process from last checkpoint to safe point
-                process_to = safe_duration - 6  # 6s safety margin for MKV tail
-                if process_to <= processed_time:
+                process_to = safe_duration - 2
+                if process_to <= processed_time + 0.5:
                     continue
 
                 log.info("Scene detection: %.1fs → %.1fs", processed_time, process_to)
@@ -112,9 +114,12 @@ class StreamManager:
 
                 if new_frames:
                     frame_count += len(new_frames)
+                    idle_cycles = 0  # reset — check again quickly
                     log.info("Found %d new scene frames (total: %d)", len(new_frames), frame_count)
                     if self._on_new_frames:
                         self._on_new_frames(new_frames)
+                else:
+                    idle_cycles += 1  # back off: 2s, 4s, 8s, 10s
 
                 processed_time = process_to
 
@@ -125,13 +130,23 @@ class StreamManager:
         self._threads["scene_detector"] = t
 
     def _estimate_safe_duration(self):
-        """Estimate recording duration. Uses ffprobe, falls back to file size."""
+        """Estimate recording duration. Uses ffprobe, falls back to file size.
+
+        For fragmented MP4 (empty_moov), format-level duration is 0 so we
+        check stream duration from the last video stream instead.
+        """
         try:
             import ffmpeg as ffmpeg_lib
             info = ffmpeg_lib.probe(str(self.recording_path))
+            # Format duration works for non-fragmented; 0 for empty_moov fMP4
             dur = float(info.get("format", {}).get("duration", 0))
             if dur > 0:
                 return dur
+            # Fragmented MP4: check video stream duration
+            for stream in info.get("streams", []):
+                sdur = float(stream.get("duration", 0))
+                if sdur > 0:
+                    return sdur
         except Exception:
             pass
 
diff --git a/cht/stream/tracker.py b/cht/stream/tracker.py
index 6849547..d299bf6 100644
--- a/cht/stream/tracker.py
+++ b/cht/stream/tracker.py
@@ -1,15 +1,13 @@
 """
-RecordingTracker: monitors the growing recording file and estimates duration.
+RecordingTracker: monitors the growing recording file and reports duration.
 
-Polls file size periodically. Uses ffprobe occasionally for accurate
-duration calibration. Feeds duration updates to the Timeline.
+Probes with ffprobe every cycle. No bitrate estimation — initial burst frames
+make calibration unreliable. Falls back to file-size heuristic only when
+ffprobe returns nothing (e.g. file too new).
 """
 
-import json
 import logging
-import subprocess
 import time
-from pathlib import Path
 from threading import Thread
 
 import ffmpeg as ffmpeg_lib
@@ -18,13 +16,12 @@ log = logging.getLogger(__name__)
 
 
 class RecordingTracker:
-    """Tracks a growing recording file and estimates its duration."""
+    """Tracks a growing recording file and reports its duration."""
 
     def __init__(self, recording_path, on_duration_update=None):
         self._path = recording_path
         self._on_duration = on_duration_update
         self._duration = 0.0
-        self._avg_bitrate = None  # bytes per second, calibrated by ffprobe
         self._stop = False
         self._thread = None
 
@@ -43,9 +40,6 @@ class RecordingTracker:
         log.info("RecordingTracker stopped")
 
     def _poll_loop(self):
-        probe_interval = 0  # probe on first data
-        cycles = 0
-
         while not self._stop:
             time.sleep(2)
 
@@ -56,28 +50,31 @@ class RecordingTracker:
             if size < 10_000:
                 continue
 
-            # Calibrate with ffprobe every ~30s or on first data
-            cycles += 1
-            if self._avg_bitrate is None or cycles % 15 == 0:
-                probed = self._probe_duration()
-                if probed and probed > 0 and size > 0:
-                    self._avg_bitrate = size / probed
-                    self._duration = probed
-                    log.info("Probed duration: %.1fs (bitrate: %.0f B/s)",
-                             probed, self._avg_bitrate)
-            elif self._avg_bitrate:
-                # Estimate from file size between probes
-                self._duration = size / self._avg_bitrate
-
-            if self._on_duration and self._duration > 0:
-                self._on_duration(self._duration)
+            duration = self._probe_duration()
+            if duration and duration > self._duration:
+                self._duration = duration
+                log.info("Duration: %.1fs", duration)
+                if self._on_duration:
+                    self._on_duration(self._duration)
 
     def _probe_duration(self):
-        """Use ffprobe to get accurate duration of the recording."""
+        """Probe recording duration via ffprobe."""
         try:
             info = ffmpeg_lib.probe(str(self._path))
-            duration = float(info.get("format", {}).get("duration", 0))
-            return duration
+            # Format-level duration is 0 for fragmented MP4 (empty_moov)
+            dur = float(info.get("format", {}).get("duration", 0))
+            if dur > 0:
+                return dur
+            # Fragmented MP4: check video stream duration
+            for stream in info.get("streams", []):
+                sdur = float(stream.get("duration", 0))
+                if sdur > 0:
+                    return sdur
         except Exception as e:
-            log.debug("ffprobe failed (file still growing): %s", e)
+            log.debug("ffprobe failed: %s", e)
+
+        # Last resort: file size heuristic (~500kbps for this stream type)
+        try:
+            return self._path.stat().st_size / 65_000
+        except Exception:
             return None
diff --git a/cht/ui/monitor.py b/cht/ui/monitor.py
index de2a6ec..ea7b007 100644
--- a/cht/ui/monitor.py
+++ b/cht/ui/monitor.py
@@ -179,19 +179,19 @@ class MonitorWidget(Gtk.Box):
         else:
             # Scrub mode
             if current == "live":
-                # Transitioning from live: seek review player to live position
+                # Transitioning from live: load MKV at cursor position atomically
                 pos = s.cursor  # already set by toggle_live()
                 if self._review_player and self._recording_path:
-                    self._review_player.load(self._recording_path)
-                    if s.paused:
-                        self._review_player.show_frame_at(pos)
-                    else:
-                        self._review_player.seek(pos)
+                    self._review_player.load_at(self._recording_path, pos, pause=s.paused)
+                    if not s.paused:
                         self._review_player.play()
                 self._stack.set_visible_child_name("review")
             else:
-                # Already in review: just apply paused state
+                # Already in review: seek if cursor moved, then apply pause/play
                 if self._review_player:
+                    player_pos = self._review_player.time_pos or 0
+                    if abs(s.cursor - player_pos) > 1.0:
+                        self._review_player.seek(s.cursor)
                     if s.paused:
                         self._review_player.pause()
                     else:
diff --git a/cht/ui/mpv.py b/cht/ui/mpv.py
index a2bd257..005a904 100644
--- a/cht/ui/mpv.py
+++ b/cht/ui/mpv.py
@@ -92,6 +92,12 @@ class Player:
         log.info("mpv load: %s", path)
         self._player.loadfile(str(path), mode="replace")
 
+    def load_at(self, path, seconds, pause=True):
+        """Load a file and seek to position atomically. Avoids async seek race."""
+        log.info("mpv load_at: %s at %.1fs pause=%s", path, seconds, pause)
+        self._player["pause"] = pause
+        self._player.loadfile(str(path), mode="replace", start=str(seconds))
+
     def load_live(self, url):
         """Load a live stream URL with low-latency options."""
         self._player["cache"] = "no"
diff --git a/cht/ui/timeline.py b/cht/ui/timeline.py
index 0e7d21c..b80ae0c 100644
--- a/cht/ui/timeline.py
+++ b/cht/ui/timeline.py
@@ -10,7 +10,6 @@ consumers read timeline.state directly.
 """
 
 import logging
-import time
 from dataclasses import dataclass, field
 
 import gi
@@ -88,7 +87,9 @@ class Timeline(GObject.Object):
         """Go to live mode at the recording end."""
         self.state.live = True
         self.state.paused = False
-        self.state.cursor = self.state.duration
+        if self.state.duration > 0:
+            self.state.cursor = self.state.duration
+        # else: keep current cursor (tick_live will continue from here)
         self._emit()
 
     def toggle_live(self, live_player_pos=None):
@@ -102,12 +103,17 @@ class Timeline(GObject.Object):
             self.state.live = False
             self.state.paused = True
             if live_player_pos is not None and live_player_pos > 0:
-                pos = max(0.0, min(live_player_pos, self.state.duration))
+                pos = max(0.0, live_player_pos)
+                # Only clamp to duration if duration is known
+                if self.state.duration > 0:
+                    pos = min(pos, self.state.duration)
                 self.state.cursor = pos
         else:
             self.state.live = True
             self.state.paused = False
-            self.state.cursor = self.state.duration
+            if self.state.duration > 0:
+                self.state.cursor = self.state.duration
+            # else: keep current tick-based cursor, set_duration will snap later
         self._emit()
 
     def play(self):
@@ -138,35 +144,28 @@ class Timeline(GObject.Object):
 
 
 class TimelineControls(Gtk.Box):
-    """Shared slider + play/pause/live controls.
+    """Slider + LIVE toggle. Scrub mode is always paused (seek-only, like a video editor).
 
-    Play/Pause and slider are insensitive in live mode.
     LIVE button is a toggle — active style when live=True.
+    Slider is insensitive in live mode.
     """
 
     def __init__(self, timeline, **kwargs):
         super().__init__(orientation=Gtk.Orientation.HORIZONTAL, spacing=4, **kwargs)
         self._timeline = timeline
-        self._updating_slider = False
         self._dragging = False
-        self._wall_clock_start = None
 
         self.set_margin_start(4)
         self.set_margin_end(4)
         self.set_margin_top(2)
         self.set_margin_bottom(4)
 
-        # Play/Pause button
-        self._play_btn = Gtk.Button(label="Play")
-        self._play_btn.connect("clicked", self._on_play_clicked)
-        self.append(self._play_btn)
-
         # Current time label
         self._time_label = Gtk.Label(label="00:00")
         self._time_label.set_width_chars(6)
         self.append(self._time_label)
 
-        # Slider
+        # Slider — disabled in live mode, scrub-seeks on release
         self._slider = Gtk.Scale(orientation=Gtk.Orientation.HORIZONTAL)
         self._slider.set_hexpand(True)
         self._slider.set_range(0, 1)
@@ -193,16 +192,8 @@ class TimelineControls(Gtk.Box):
         timeline.connect("changed", self._on_changed)
         GLib.timeout_add(1000, self._tick_total)
 
-    def _on_play_clicked(self, btn):
-        s = self._timeline.state
-        if s.paused:
-            self._timeline.play()
-        else:
-            self._timeline.pause()
-
     def set_live_toggle_callback(self, cb):
-        """Override the LIVE button handler. cb() should return the live player
-        position (float or None) and call timeline.toggle_live() itself."""
+        """Override the LIVE button handler."""
         self._live_toggle_cb = cb
 
     def _on_live_clicked(self, btn):
@@ -226,12 +217,6 @@ class TimelineControls(Gtk.Box):
     def _on_changed(self, timeline):
         s = timeline.state
 
-        # Start wall clock when first going live (not on duration, which arrives ~30s later)
-        if s.live and self._wall_clock_start is None:
-            self._wall_clock_start = time.monotonic()
-
-        # Live mode: disable scrub controls
-        self._play_btn.set_sensitive(not s.live)
         self._slider.set_sensitive(not s.live)
 
         if s.live:
@@ -239,15 +224,9 @@ class TimelineControls(Gtk.Box):
         else:
             self._live_btn.remove_css_class("suggested-action")
 
-        # Play button label (only relevant in scrub mode)
-        self._play_btn.set_label("Pause" if not s.paused else "Play")
-
-        # Slider position
         if not self._dragging:
-            self._updating_slider = True
             self._slider.set_range(0, max(s.duration, 0.1))
             self._slider.set_value(s.cursor)
-            self._updating_slider = False
 
         self._time_label.set_text(self._fmt_time(s.cursor))
         self._update_duration_label()
@@ -258,10 +237,8 @@ class TimelineControls(Gtk.Box):
 
     def _update_duration_label(self):
         s = self._timeline.state
-        loaded = s.duration
-        total = (time.monotonic() - self._wall_clock_start) if self._wall_clock_start else loaded
         self._duration_label.set_text(
-            f"{self._fmt_time(loaded)} / {self._fmt_time(total)}"
+            f"{self._fmt_time(s.cursor)} / {self._fmt_time(s.duration)}"
         )
 
     @staticmethod
diff --git a/cht/window.py b/cht/window.py
index 7d9820f..b31df6e 100644
--- a/cht/window.py
+++ b/cht/window.py
@@ -25,6 +25,7 @@ class ChtWindow(Adw.ApplicationWindow):
         self.set_title(APP_NAME)
         self.set_default_size(1400, 900)
         self._streaming = False
+        self._gone_live = False
         self._stream_mgr = None
         self._tracker = None
         self._known_frames = set()
@@ -72,6 +73,7 @@ class ChtWindow(Adw.ApplicationWindow):
         self._connect_btn.remove_css_class("suggested-action")
         self._connect_btn.add_css_class("destructive-action")
         self._streaming = True
+        self._gone_live = False
 
         # Create session
         self._stream_mgr = StreamManager()
@@ -91,15 +93,11 @@ class ChtWindow(Adw.ApplicationWindow):
         )
         self._tracker.start()
 
-        # Go LIVE after a short delay — ffmpeg needs time to establish TCP
-        # and begin writing both outputs. UDP relay starts immediately after.
-        GLib.timeout_add(4000, self._go_live_once)
-
         # Start scene detection
         self._stream_mgr.start_scene_detector(on_new_frames=self._on_new_scene_frames)
 
         # Start polling for frame thumbnails
-        GLib.timeout_add(3000, self._poll_frames)
+        GLib.timeout_add(1000, self._poll_frames)
 
         # Tick the LIVE cursor every second
         GLib.timeout_add(1000, self._tick_live)
@@ -123,6 +121,9 @@ class ChtWindow(Adw.ApplicationWindow):
     def _on_duration_update(self, duration):
         """Called from RecordingTracker thread."""
         GLib.idle_add(self._timeline.set_duration, duration)
+        if not self._gone_live:
+            self._gone_live = True
+            GLib.idle_add(self._go_live_once)
 
     def _on_new_scene_frames(self, frames):
         """Called from scene detector thread when new frames are found."""
@@ -223,7 +224,8 @@ class ChtWindow(Adw.ApplicationWindow):
         # Horizontal scrolling strip — storyboard style
         self._frames_scroll = Gtk.ScrolledWindow()
         self._frames_scroll.set_policy(Gtk.PolicyType.AUTOMATIC, Gtk.PolicyType.NEVER)
-        self._frames_scroll.set_min_content_height(180)  # 144px thumb + label + padding
+        self._frames_scroll.set_min_content_height(168)
+        self._frames_scroll.set_size_request(-1, 168)  # 144px thumb + label + padding
 
         self._frames_strip = Gtk.Box(orientation=Gtk.Orientation.HORIZONTAL, spacing=4)
         self._frames_strip.set_margin_start(4)
@@ -366,9 +368,10 @@ class ChtWindow(Adw.ApplicationWindow):
         label.set_ellipsize(Pango.EllipsizeMode.END)
         box.append(label)
 
-        # Click to seek into scrub mode
+        # Click to highlight — does NOT switch mode or seek
+        # (future: jump to timestamp in scrub bar without leaving live)
         gesture = Gtk.GestureClick()
-        gesture.connect("released", lambda g, n, x, y: self._timeline.seek(timestamp))
+        gesture.connect("released", lambda g, n, x, y: log.debug("Frame clicked: %s at %.1fs", frame_id, timestamp))
         box.add_controller(gesture)
 
         self._frames_strip.append(box)
diff --git a/sender/stream_av.sh b/sender/stream_av.sh
index b0d7551..b497c6d 100755
--- a/sender/stream_av.sh
+++ b/sender/stream_av.sh
@@ -30,12 +30,12 @@ if [ -n "$WEBCAM_MIC" ]; then
     exec ffmpeg \
         -init_hw_device drm=drm:/dev/dri/card0 \
         -init_hw_device vaapi=va@drm \
-        -device /dev/dri/card0 -f kmsgrab -i - \
+        -device /dev/dri/card0 -f kmsgrab -framerate 30 -i - \
         -f pulse -i "$MONITOR" \
         -f pulse -i "$WEBCAM_MIC" \
         -filter_complex "[1:a][2:a]amix=inputs=2:duration=longest[aout]" \
         -map 0:v -map "[aout]" \
-        -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12' \
+        -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12,fps=30' \
         -c:v h264_vaapi -qp 20 -g 30 -keyint_min 30 -bf 0 \
         -c:a aac -b:a 128k \
         -flush_packets 1 -fflags nobuffer -muxdelay 0 -muxpreload 0 \
@@ -46,9 +46,9 @@ else
     exec ffmpeg \
         -init_hw_device drm=drm:/dev/dri/card0 \
         -init_hw_device vaapi=va@drm \
-        -device /dev/dri/card0 -f kmsgrab -i - \
+        -device /dev/dri/card0 -f kmsgrab -framerate 30 -i - \
         -f pulse -i "$MONITOR" \
-        -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12' \
+        -vf 'hwmap=derive_device=vaapi,scale_vaapi=w=1920:h=1080:format=nv12,fps=30' \
         -c:v h264_vaapi -qp 20 -g 30 -keyint_min 30 -bf 0 \
         -c:a aac -b:a 128k \
         -flush_packets 1 -fflags nobuffer -muxdelay 0 -muxpreload 0 \