import re


def youtube(link):
    """Find youtube player URL."""
    pattern = r'http://www\.youtube\.com\/watch\?v=([a-zA-Z0-9\-\_]+)'
    match = re.match(pattern, link)
    if not match:
        pattern = r'http:\/\/youtu.be\/([a-zA-Z0-9\-\_]+)'
        match = re.match(pattern, link)
    if not match:
        return None
    return 'http://www.youtube.com/embed/%s' % match.group(1)