The victims, who allegedly had links with Syrian security forces, were executed in the Bab al-Neirab neighborhood of the northwestern city of Aleppo.
The video was posted by the Syrian Observatory for Human Rights, which is based in London.
On January 29, Syrian security forces discovered the bodies of more than 80 people in the city.
The bodies of young men and boys, killed execution-style, were found in the Quweiq River – southwest of Aleppo – which is under the control of the militants.
A large number of similar executions have been carried out by the militant groups over the past months, drawing condemnation from human rights groups.
However, the West and some regional countries that support the militants have failed to condemn the killings.
The crisis began in Syria in March 2011. Many people, including large numbers of army and security personnel, have been killed ever since.
On Saturday, an explosive device planted underneath a vehicle detonated near al-Hijaz Square in the capital, Damascus. One person was killed and two others injured in the bombing.
The Syrian government says the West and its regional allies Qatar, Saudi Arabia, and Turkey are supporting the armed groups. There are also reports that a very large number of the militants are foreign nationals.
Several international human rights organizations have also accused the militants of committing war crimes.
The UN Refugee Agency said on February 1 that nearly 45,000 displaced Syrians were living in “appalling” conditions in an area of the north of the country held by militants.