In the video, posted to YouTube
on Wednesday, a crew member in the front of the airship records the pilot flying the helicopter and two men in the back of the craft pushing four barrels out the back.
Several canisters that appear to be barrel bombs -- oil drums filled with explosives and shrapnel -- are dropped from the chopper.
CNN cannot independently confirm the authenticity of the events described by opposition group SMO.
Syrian President Bashar al-Assad, in an interview with the BBC in February, categorically denied any use of barrel bombs by his forces.
Great Britain said the video -- recovered after the helicopter was shot down and members of its crew captured, according to SMO -- shows "criminal acts" against civilians.
"This video footage exposes Assad's lies on barrel bombs. It shows the casual and indiscriminate way in which Syrian regime forces are dropping these horrific weapons out of helicopters onto civilians below," UK Foreign Secretary Philip Hammond said.
Earlier this month, rights group Amnesty International alleged in a report
that Syrian government forces had killed and wounded civilians by dropping barrel bombs on schools, hospitals, mosques and crowded markets in opposition-controlled areas of Aleppo.
Attacks using barrel bombs killed more than 3,000 civilians in Aleppo governorate last year, the report said, and have helped create a climate of fear.
The U.N. Security Council unanimously adopted a resolution on Syria in February 2014 demanding "that all parties immediately cease all attacks against civilians, as well as the indiscriminate employment of weapons in populated areas, including shelling and aerial bombardment, such as the use of barrel bombs."
SMO said the video was recorded in March in the Zawiya Mountains in Idlib province.
In March, several media outlets reported the downing of a helicopter in Syria and posted photos supposedly taken at the site. At the end of the video posted by SMO, there is about six seconds of a helicopter lying on its side. The video did not make clear whether the images are of the same aircraft.