Hello J. Truong,

Can you please provide a link to a webpage where you experience this difficulty?

Many thanks,

Paul

http://www.thucday2020.com/-bs-m-t-james-tr--ng-w1-12-2015.html

Thank you.  I have visited the page in question and have not found any difficulty in using the media files, starting and stopping them as required without any duplication in sound, etc.

Can you advise what browser you are using when you experience the issue?