The former commander of a Serbian police unit called the Scorpions, accused of shooting six Bosnian Muslims dead, has denied any involvement.
The video shows the bound victims marched into the woods and shot
Slobodan Medic, on trial with four others in Belgrade, said he would have killed the soldier who filmed the shootings had he foreseen the impact.
He denied either being present or ordering the killings, which happened during the 1995 Srebrenica massacre.
The film shocked Serbs when it aired in June and led to the suspects' arrest.
This is the first trial in Serbia to deal with the massacre of nearly 8,000 Muslim men and boys around Srebrenica and is the biggest war crimes trial of Serbs by Serbs.
At the time, Mr Medic told the court, the video had seemed "irrelevant".
"Now it can cost me my freedom," he added.
Had he known that the footage would become public, he would have "killed like a rabbit" the Serb soldier who filmed the killings, he said.
He insisted that he did not order the killings, but he said he could not control soldiers who wanted to avenge family members killed by Muslims.
The video apparently shows the accused leading the Bosnian Muslim captives into a wood to be shot.
Mr Medic is the first of the five defendants to make his case, after the trial opened on Tuesday morning.
The men are accused of crimes against humanity and of violating the customs of war.
Relatives of the victims from Srebrenica attended the opening of the trial, and watched from behind bullet-proof glass.
Relatives of the defendants were also there.
The video - which lasts about 20 minutes - shows several members of the Scorpions unit ordering the six prisoners, dressed in civilian clothes, from the back of a lorry.
The victims are marched into woodland and shot one by one.
Srebrenica - a UN-protected enclave - fell to Bosnian Serb forces towards the end of the Bosnian war. The subsequent massacre was the worst atrocity in Europe since 1945.
The men in court were arrested in June, days after the footage was shown at the trial of former Serbian President Slobodan Milosevic at The Hague.
The other four accused are Pero Petrasevic, Aleksandar Medic, Branislav Medic and Aleksandar Vukov.
They face up to 40 years in jail if found guilty.
"There is no death sentence, but I hope justice will be served for those monsters," said Sajma Saltic, whose brother Sadik, 36, was among the victims identified on the video.
A sixth suspect has already been on trial for war crimes in Croatia, while a seventh has not been found.
Both the former Bosnian Serb leader Radovan Karadzic and his military counterpart, Ratko Mladic, are accused by the international war crimes tribunal in The Hague of orchestrating genocide at Srebrenica.
They remain Europe's two most wanted fugitives and are considered heroes by Serb nationalists.
Next year the tribunal in The Hague is due to put nine former Bosnian Serb officers on trial jointly for the Srebrenica massacre. Eight of them are in the tribunal's custody.