I can offer some advice in this area. I am not an expert, but my wife was hesitant and it took careful calculations to get from point A to point B.
First of all if your woman is like my wife, she is hot yet prudent, sexy but has morals and far from a slut.
Now the reason for the tapes and pics:
20 years from now you will want to look back on these items and remeber what it was like to be young and beautiful. Also, God forbid, what if something happened to your girl? A freak Accident? Where would you go for pleasure and what would you do to remember all of the sexy nights you had? When I asked my wife to consider this, she agreed to cooperate with lingerie modeling, and strip teases on tape. Sometimes the strip teases would lead to foreplay and sex, so I left the camera running and it was on a stand - boom.
Now I have learned this: she doesn't care about the tapes, she doesn't want to watch them, they are for me and for my entertainment.
So you might try ..."if anything ever happened to you, at least I would have something to remember some of our sexy times together..." of course, they are private and you could never show them to anyone for any reason.
Try this approach and it should help get you started.