input: Write a function to extract titles of all YouTube videos from a given URL. The function will use the requests library to fetch the webpage content and the re library to extract the video titles using regular expressions. If no titles are found or an error occurs during the process, the function should return an empty list.
  
  def extract_youtube_titles(url):
      try:
          r = requests.get(url)
          titles = re.findall('<a href="/watch\?v=([^"]+)">(.+?)<\/a>', r.content.decode('utf-8'))
          return [title[1] for title in titles]
      except Exception as e:
          return []
  
  # Test cases
  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/NoVideosHere/videos") == []
  assert extract_youtube_titles("invalid_url") == []
output: def extract_youtube_titles(url):
      try:
          r = requests.get(url)
          titles = re.findall('<a href="/watch\?v=([^"]+)">(.+?)<\/a>', r.content.decode('utf-8'))
          return [title[1] for title in titles]
      except Exception as e:
          return []