input: Write a function to extract titles of all YouTube videos from a given URL. The function should use requests and re libraries to fetch the webpage content and extract the video titles. Return a list of video titles. If the URL is invalid or no titles are found, return an empty list.
  
  assert extract_youtube_titles("https://www.youtube.com/user/Thexvid/videos")==["First Video Title", "Second Video Title", "Third Video Title"]
  assert extract_youtube_titles("https://www.youtube.com/user/InvalidUser/videos")==[]
  assert extract_youtube_titles("https://www.invalidwebsite.com")==[]
output: def extract_youtube_titles(url):
      import requests
      import re
      try:
          response = requests.get(url)
          if response.status_code != 200:
              return []
          html_content = response.text
          titles = re.findall(r'<a[^>]*aria-label="([^"]+)"', html_content)
          return [title for title in titles if "YouTube" not in title]
      except:
          return []