First, my condolences. I cannot imaging the pain your family is facing.
Second, I will concur with other posters. Don't focus so much on preserving your wife into the future that you forget to make memories now.
That said, I am having my family do something proactively that might be of service. Particularly with my mother (who at 64 isn't exactly old yet, but anything can happen).
Write letters. I mean the hand-written kind. One for birthdays, graduations, weddings, first jobs, grandchildren, and other major events. It will be difficult to do, but tell your wife to mentally take a trip to the future. She's watched her kids grow up and now face an important life event. What would she like to say to them? Advice? Congratulations? Stories? I would suggest having your wife do this in chronological order, giving her the opportunity to mentally and emotionally age the kids and take a mental stroll through their future.
You didn't mention your children's gender, but if they are girls I would also suggest those letters cover some of the mother/daughter talks about growing up. Menstruation, first boyfriend, first kiss... you get the idea.
Video is good, but sometimes they are hard to watch. And, as others have already commented, letting go and letting time dull the memories is just as important as remembering. The past is a great place to visit, but you can't live there.
After you wife has passed, you will be her representative. She can't parent from the grave (apologies if that sounds cold) simply because there isn't a 2-way conversation. But at least with these letters she can share her most important thoughts directly with the kids... and give you a starting place.