North Korea is accused of faking footage that showed a ballistic missile successfully launching from a submarine.
A California-based think tank analysed the footage which was released on North Korean state television days after the country said it had also conducted a fourth nuclear test.
Researchers at Middlebury Institute noted that a number of well-known techniques had been used to manipulate the footage.
"The rocket ejected, began to light, and then failed catastrophically," said one of the body’s senior researchers Melissa Hanham.
It is claimed that the video shows two frames where flames engulf the missile and small parts of its body break away.
"North Korea used heavy video editing to cover over this fact," Hanham said.
"They used different camera angles and editing to make it appear that the launch was several continuous launches, but played side by side you can see that it is the same event".
North Korean propagandists supposedly used rudimentary editing techniques to crop and flip old video footage of an earlier missile test and Scud missile launch, the video analysis showed.
Although South Korea's military said that the video appeared to have been modified with Scud missile footage from 2014, an official admitted that the ejection technology might have improved since the May test.
The North's recent claim that its fourth and most recent nuclear test was of a more advanced and powerful hydrogen bomb has also drawn scepticism from experts.
Last month, satellite images emerged of a North Korean rocket deployment site that had been upgraded to enable it to launch larger rockets.