reset fps to 1 + change bg_color in fig

app.py

@@ -18,7 +18,7 @@ def extract_waveform_animation(audio_file, window_seconds=5):
     first_window = y[:window_length]
     x_vals = np.linspace(0, duration, num=len(y))
     ax.set_axis_off()
-    ax.set_facecolor("black")
+    fig.set_facecolor("black")
     
     def init():
         ax.set_xlim(0, window_seconds)
@@ -43,7 +43,7 @@ def extract_waveform_animation(audio_file, window_seconds=5):
                        init_func=init, interval=7, blit=False)
     
     with tempfile.NamedTemporaryFile(delete=False, suffix='.mp4') as tmpfile:
-        ani.save(tmpfile.name, writer='ffmpeg', fps=30)
+        ani.save(tmpfile.name, writer='ffmpeg', fps=1)
         video_path = tmpfile.name
     
     return video_path