From My post https://stackoverflow.com/a/48072230/7576100
More Tutorial here- www.JaneshSwift.com

----------**Swift 4+**-------

Example for audio/mp3 detect -

*Step 1:* Use delegate

    class ViewController : WKUIDelegate,WKNavigationDelegate {

*Step 2:* Setting WebKit

     func setWebView() {
            let webConfiguration = WKWebViewConfiguration()
            webView = WKWebView(frame: .zero, configuration: webConfiguration)
            webView.uiDelegate = self
            webView.navigationDelegate = self
            view = webView
   
            let myURL = URL(string: "https://www.bossmobi.guru/files/download/type/320/id/197255")//your audio url
            let myRequest = URLRequest(url: myURL!)
            webView.load(myRequest)
        }
*Step 3:* Get audio MIME type from webkit delegate.

     func webView(_ webView: WKWebView, decidePolicyFor navigationResponse: WKNavigationResponse, decisionHandler: @escaping (WKNavigationResponsePolicy) -> Void) {
            print( #function + "url is \(String(describing: webView.url))"  + "Mimetype" + "\(navigationResponse.response.mimeType ?? "NotAvailable")")
            if let _ = navigationResponse.response.mimeType?.range(of: "audio/mpeg") {
                print("MP3 is audio url \(String(describing: webView.url))")
                webView.stopLoading()
            }
            decisionHandler(.allow)
        }


---------**ObjC**----------

**WKWebView setup**

      NSString *urlString = @"https://www.bossmobi.guru/files/download/type/320/id/197255";
   
        WKWebViewConfiguration *theConfiguration = [[WKWebViewConfiguration alloc] init];
        WKWebView *_demoWKWebView = [[WKWebView alloc] initWithFrame:self.view.frame configuration:theConfiguration];
        _demoWKWebView.navigationDelegate = self;
        _demoWKWebView.UIDelegate = self;
        NSURL *nsurl=[NSURL URLWithString:urlString];
        NSURLRequest *nsrequest=[NSURLRequest requestWithURL:nsurl];
        [_demoWKWebView loadRequest:nsrequest];
        [self.view addSubview:_demoWKWebView];

**WKWebView delegate**

    -(void)webView:(WKWebView *)webView decidePolicyForNavigationResponse:(WKNavigationResponse *)navigationResponse decisionHandler:(void (^)(WKNavigationResponsePolicy))decisionHandler {
        //NSLog(@"decidePolicyForNavigation---Response  %@",webView.URL);
        if ([navigationResponse.response.MIMEType isEqualToString:@"audio/mpeg"]) {
            NSLog(@"MP3  audio url is %@",webView.URL);
        }
        decisionHandler(WKNavigationResponsePolicyAllow);
    }