performance improvement

sam-tool-tauri/src/components/extract/FrameCanvas.tsx

@@ -16,7 +16,10 @@ export const FrameCanvas = forwardRef<HTMLCanvasElement, Props>(function FrameCa
         className="canvas-frame"
         style={{ aspectRatio: `${video.width} / ${video.height}` }}
       >
-        <canvas ref={ref} width={video.width} height={video.height} />
+        {/* Backing-store width/height are set imperatively in drawBitmap so we
+            can cap it at the displayed (CSS) size × DPR — drawing 4K every frame
+            into a 1080p window is the main playback cost on slow systems. */}
+        <canvas ref={ref} />
         {extracted && (
           <div className="frame-extracted-banner">EXTRACTED</div>
         )}