Whether or not it is legal to make a video tape of anyone without informing them depends on the state that you are in. In some jurisdictions, it is legal to make video recordings, but not video recordings with audio.
That being said, though, if you make a video recording of you and your wife having sex without her knowing it and post it on the Internet, your wife could sue you for invasion of privacy and false light in the public eye, and intentional infliction of emotional distress. Those are all torts that allow the recovery of punitive damages. Furthermore, if you have children and end up divorced because you posted a tape like this on the internet, the family court could consider this in deciding who gets custody -- and it's not going to be against the spouse who thought she was having consensual sex in the privacy of her own home.
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