Write an iPhone function

Hello, We have an iOS application, the application exports a video for users (a one minute video), we are looking for a freelancer to write a function for us so we can include subtitles on the video (subtitles that will change with time of course during the one minute). Again in simple terms, the function should add words on top of the video (overlay) and the words will change with time, for example, we have 10 words to show during the one minute video, each word will have a specific time, word 1 will be shown from (0:00 to 0:03) while word two (0:03 to 0:08 for example) and so on. Please type TextOnVideo in your bid so I know you're read it all. Thanks.