refactor update function for windowed view

app.py

@@ -26,11 +26,11 @@ def extract_waveform_animation(audio_file):
     def update(frame):
         start = frame * sr
         end = min(start + sr, len(y))
-        line.set_data(np.linspace(0, duration, num=len(y[:end])), y[:end])
+        line.set_data(np.linspace(start, end, num=len(y[:end])), y[:end])
         return line,
     
     # Create the animation
-    ani = FuncAnimation(fig, update, frames=np.arange(0, int(duration)), init_func=init, interval=7, blit=False)
+    ani = FuncAnimation(fig, update, init_func=init, interval=7, blit=False)
     
     # Save the animation to a temporary file
     with tempfile.NamedTemporaryFile(delete=False, suffix='.mp4') as tmpfile: