The case sparked protests on the university campus, where the four were students.
"After listening to presentations by both parties, the court has found the accused guilty as charged," magistrate Mziwonke Hinxa said.
One clip showed a young man appearing to urinate into a bowl of stew and then serving it to the housekeepers.
The video sparked an international scandal when it appeared on the internet in February 2008.
In a statement the boys denied urinating on the food, saying: "It was an act meant to look like urine."
"This case must send a message that disrespecting older people is a crime"
Johan Kruger, the state prosecutor
Defence lawyer Kemp J Kemp told the court that the students had not intended to humiliate the housekeepers, but later realised they had done just that.
"The accused did not realise the effect of the video and what it would have on the university and the plaintiffs. They now, in retrospect, accept that the use of the workers for the video was insensitive, ill considered and wrong," he said.
Johan Kruger, the state prosecutor, had asked the magistrate to fine the four saying: "This case must send a message that disrespecting older people is a crime."
The video was shot at a time when the University of Free State was introducing racial integration at student hostels, following decades of race-based hostel allocation.
The students' film ended with the words: "That, at the end of the day, is what we think of integration."
In October last year, university rector Jonathan Jansen came under fire when he announced that the institution was withdrawing disciplinary charges against the students, in an attempt to promote reconciliation.