fix no or invalid link

app.py

@@ -1,10 +1,13 @@
-import gradio as gr, glob, os, auditok, random, zipfile, wave
+import gradio as gr, glob, os, auditok, random, zipfile, wave, pytube.exceptions
 from pytube import YouTube
 from moviepy.editor import VideoFileClip
 import auditok
 
 def download_video(url):
-    yt = YouTube(url)
+    try:
+        yt = YouTube(url)
+    except pytube.exceptions.RegexMatchError:
+        raise gr.Error("URL not valid or is empty! Please fix the link or enter one!")
     video = yt.streams.get_highest_resolution()
     video.download()
     video_path = f"{video.default_filename}"