Danielle Hirst, 29, and Craig Smith, 31, both of Bridlington, were captured on CCTV in Domino's Pizza, in Castle Road, Scarborough, getting intimate.
The Crown Prosecution Service showed the 18-minute video in court.
The X-rated footage showed the couple engaging in the act while staff worked on the other side of the counter.
But ahead of the act it shows them carrying out lewd simulations with a large cone and Smith lifting Hirst into the air.
Hirst appeared visibility embarrassed, hiding behind her sleeves and at times couldn't look at the footage.
Chairman of the bench, Angela Beardshall, said the footage showed their "lewd, obscene and disgusting" actions.
She added: "The offence was in a public place. Members of the public were present and so were staff.
"Members of the public should not have to put up with this disgusting behaviour."
Hirst, of Gypsey Road, Bridlington, had changed her plea to guilty of outraging public decency by behaving in an indecent manner, namely by having sexual intercourse.
But her partner, Smith, of Field Road, was found guilty when the case was tried in his absence due to him being remanded in custody on other offences.
They were told by magistrates that the offence was so serious they have not ruled out a custodial sentence.
The pair are due back at Scarborough Magistrates' Court for sentencing on October 17.