1. You can download videos from other video sites. I recommend to use your local community web sites instead of popular ones.
2. Run your video editing software. The best one I found for myself is Sony Vegas. Open your video file, add second video track and insert text there, I mean the link to your web site or any other text you may wish to add. Stretch it for the whole video, not in the beginning only or in the end only. Render the created video to a new video file. You should try different codecs/settings to find a balanced solution for good quality and not too big file size.
I recommend you to cloak your affiliate link. Buy some short domain name and redirect it to your link. Or at least use subdomain of free hosting/blogspot, but try to keep it short. If you put the whole affiliate link on your video you will get less visits, people are lazy creatures actually.
Ok. My fast thoughts about what you asked. Upload short videos to youtube with your link. Dude comes to your link where you write that in order to get this video in full he must complete the offer xxxxxx and then on some finish page take the 3-d word from the 5-th line and use it as a password to get access to your password protected directory where you host full videos. Or he could send a text message to a premium rate number to get a password and so on (not all countries covered though).
Well I hope it will give you some ideas