Share pixbufs between frames panel and scrub bar — single disk read per frame

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cht/ui/scrub_bar.py

@@ -131,24 +131,39 @@ class ScrubBar(Gtk.DrawingArea):
         self.queue_draw()
 
     def add_frame(self, timestamp: float, path: str) -> None:
-        """Add a single frame thumbnail incrementally."""
+        """Add a single frame thumbnail from file path."""
         if not Path(path).exists():
             return
         thumb_h = BAR_HEIGHT - 4
         thumb_w = int(thumb_h * 16 / 9)
         try:
             pixbuf = GdkPixbuf.Pixbuf.new_from_file_at_scale(path, thumb_w, thumb_h, True)
-            surface = self._pixbuf_to_surface(pixbuf)
-            self._frame_thumbs.append({
-                "timestamp": timestamp,
-                "surface": surface,
-                "width": pixbuf.get_width(),
-                "height": pixbuf.get_height(),
-            })
-            self.queue_draw()
+            self.add_frame_from_pixbuf(timestamp, pixbuf)
         except Exception as e:
             log.debug("Thumb load failed for %s: %s", path, e)
 
+    def add_frame_from_pixbuf(self, timestamp: float, pixbuf) -> None:
+        """Add a single frame thumbnail from an already-loaded pixbuf (shared with frames panel)."""
+        thumb_h = BAR_HEIGHT - 4
+        thumb_w = int(thumb_h * 16 / 9)
+        scaled = pixbuf.scale_simple(thumb_w, thumb_h, GdkPixbuf.InterpType.BILINEAR)
+        surface = self._pixbuf_to_surface(scaled)
+        self._frame_thumbs.append({
+            "timestamp": timestamp,
+            "surface": surface,
+            "width": scaled.get_width(),
+            "height": scaled.get_height(),
+        })
+        self.queue_draw()
+
+    def set_frames_from_pixbufs(self, frames: list[dict]) -> None:
+        """Bulk set thumbnails from already-loaded pixbufs. Each dict: {timestamp, pixbuf}."""
+        self._frame_thumbs = []
+        for f in frames:
+            self.add_frame_from_pixbuf(f["timestamp"], f["pixbuf"])
+        # queue_draw already called per frame, but one more to be safe
+        self.queue_draw()
+
     @staticmethod
     def _pixbuf_to_surface(pixbuf):
         """Convert a GdkPixbuf to a cairo ImageSurface."""

cht/window.py

@@ -647,9 +647,9 @@ class ChtWindow(Adw.ApplicationWindow):
             self._frames_panel.load_items(items)
             self._known_frames = {item["id"] for item in items}
             self._agent_output.append(f"  Loaded {len(items)} frame thumbnails.\n")
-            # Update scrub bar thumbnails
-            self._timeline_controls.scrub_bar.set_frames(
-                [{"timestamp": e["timestamp"], "path": str(e["path"])} for e in entries]
+            # Update scrub bar thumbnails — reuse already-loaded pixbufs
+            self._timeline_controls.scrub_bar.set_frames_from_pixbufs(
+                [{"timestamp": it["timestamp"], "pixbuf": it["pixbuf"]} for it in items]
             )
 
     def _load_existing_transcript(self):
@@ -676,7 +676,7 @@ class ChtWindow(Adw.ApplicationWindow):
                 pixbuf = GdkPixbuf.Pixbuf.new_from_file_at_scale(str(entry["path"]), 256, 144, True)
                 auto = self._timeline.state.live and not self._transcript_panel.has_selection
                 self._frames_panel.add_item(fid, pixbuf, entry["timestamp"], auto_select=auto)
-                self._timeline_controls.scrub_bar.add_frame(entry["timestamp"], str(entry["path"]))
+                self._timeline_controls.scrub_bar.add_frame_from_pixbuf(entry["timestamp"], pixbuf)
             except Exception as e:
                 log.warning("Thumbnail load failed for %s: %s", fid, e)
         return True