I can't find out which was the first adult movie put on videotape...but these are some of the earliest ones...
Selection from Daniel D. Teoli Jr. VHS / Betamax Archive
Selection from Daniel D. Teoli Jr. eBay Adult Only Archive
At $99 a tape, they were pretty pricey. In the early days of VHS / Beta porn they didn't put explicit photos on the covers. They would advertise in magazines, some of them mainstream video mags. Later on, when video rental shops were widespread, and they had the 'back room' for porn tapes, covers became more explicit. In the early days of videotape rental stores, they even rented out videocassette machines.
In 1972 they were renting out video equipment to film sex at home, or whatever you liked. Living through it, too bad I didn't pay more attention to that era. It would have saved some time putting the puzzle back together. NSFW link
Early Video Equipment Ad 1972 D. D. Teoli Jr. A. C. : D. D. Teoli Jr. A. C. : Free Download, Borrow, and Streaming : Internet Archive