This isn’t exactly correct. You can’t include photos and commercial movies or TV shows in the same library, but a Photo Library will include your personal videos (that you’ve taken with your camera or phone) alongside photos in the same folder. I don’t find that convenient myself – I put videos in a separate folder and create an “Other Videos” library, as JaysPlex7 suggests – but it does work.
I want to say I tried that about 5 years ago and couldn’t get it to work. Maybe I tried to combine both inside an other videos library and just assumed neither would work