Update inference.py

inference.py

@@ -118,7 +118,8 @@ if __name__ == "__main__":
     # Step 3. inference
 
     if args.is_long_video:
-        window_size = int(np.sqrt(args.video_length))
+        import math
+        window_size = int(math.sqrt(args.video_length))
         sample = pipe.generate_long_video(args.prompt + POS_PROMPT, video_length=args.video_length, frames=pil_annotation, 
                     num_inference_steps=50, smooth_steps=args.smoother_steps, window_size=window_size,
                     generator=generator, guidance_scale=12.5, negative_prompt=NEG_PROMPT,