Youtube Video Id from URL - Swift3

Basically I have a Youtube URL as string, I want to extract the video Id from that URL. I found some code in objective c that is as below:

NSError *error = NULL;
NSRegularExpression *regex = 
[NSRegularExpression regularExpressionWithPattern:@"?.*v=([^&]+)"
                                          options:NSRegularExpressionCaseInsensitive
                                            error:&error];
NSTextCheckingResult *match = [regex firstMatchInString:youtubeURL
                                                options:0
                                                  range:NSMakeRange(0, [youtubeURL length])];
if (match) {
    NSRange videoIDRange = [match rangeAtIndex:1];
    NSString *substringForFirstMatch = [youtubeURL substringWithRange:videoIDRange];
}

When I am converting this code to swift3 that is:

var error: Error? = nil
var regex = try! NSRegularExpression(pattern: "?.*v=([^&]+)", options: .caseInsensitive)
var match = regex!.firstMatch(in: youtubeURL, options: [], range: NSRange(location: 0, length: youtubeURL.length))!
if match {
    var videoIDRange = match.rangeAt(1)
    var substringForFirstMatch = (youtubeURL as NSString).substring(with: videoIDRange)
}

Gives error as:

fatal error: 'try!' expression unexpectedly raised an error: Error Domain=NSCocoaErrorDomain Code=2048 "The value “?.*v=([^&]+)” is invalid."

Can anybody help me about this error or anybody explain how to get video id from url in Swift 3.

Thanks in advance