Your question is imprecise, so I'll restate it in what I think is a meaningful way. Be sure to let me know if I misunderstood.
Under Texas state law, is it a crime to covertly record another during sexual activity, without publishing the recording?
Yes, under the Texas "Revenge Porn Law."
In 2015, the Texas State Legislature passed the Texas Revenge Porn Law which states, in relevant part:
TEXAS PENAL CODE SEC. 21.15. INVASIVE VISUAL RECORDING
* * *
(b) A person commits an offense if, without the other person's consent and with [the] intent to invade the privacy of the other person, the person:
(1) photographs or by videotape or other electronic means
records, broadcasts, or transmits a visual image of an intimate area of another person if the other person has a reasonable expectation that the intimate area is not subject to public view;
* * *
(c) An offense under this section is a state jail felony.
See
https://statutes.capitol.texas.gov/D...E.21.htm#21.16 (emhasis added). A state jail felony is punishable by up to two years in a state jail facility, a $10,000 fine, or both.
Thus, it is a crime to record such images without broadcasting them, as long as the intent requirement is met. Also, sending the images from the recording device to another electronic device would be, arguably, a "transmission," which the law also makes illegal.
(As an aside, nudity isn't required to violate Section 21.15 as long as the recording shows an "intimate area." "'Intimate area' means the naked
or clothed genitals, pubic area, anus, buttocks, or female breast of a person."
Id. (emphasis added).