I am hopeful that I'd be worth of your time, and investment for the assignment that you ask for, and since I am fluent in English (given your own observation), I will make good use of my time in aiding your effort for transcribing the audio file. As in regards for the task itself, I hope that further details are informed for my own inquiry, and much would be appreciated that you choose to hire me.
Thank you very much for taking your time in reading my proposal for my recruitment, and hope you a pleasant day.