Recording the web page by using Record RTC with Angular

I want do recording the particular part in the page as video with audio . For example when user enter the page will automatic recording what happening occurs (like iframe video )the particular part in the page and the user close the page or click the stop button will stop recording and save video to the file. Now I using Record RTC to do it and try to use canvas method still cannot. Anyone can give me suggestion and solution to do this feature . Thanks for Helping. You can edit in this page. https://stackblitz.com/edit/angular-record-rtc-demo-si2c8x