Adding unique code to videofile in adult member section (Data Processing, PHP, Script Installation, Website Security)

I want this functionality added to my adult member section: a member logs in, let's say his name is Jack. He clicks on a video file to download. Then on the server, that video file is copied from a master file, with the name Jack inserted in the video file data. While the video file is being copied and prepared on the server, Jack gets to see some message informing him he has to wait a few seconds, then when the file is ready, the download starts automatically. When this file later would be opened in a text editor, the name Jack would be visible somewhere. Despite adding this text to the video file data, the video file is still playable in video player software.

This is only the first step of a bigger plan I have, if you can help me with this first step, you can also help me with the next steps, for which the budget will be 5 to 10,000.