A public webcam from the website Viewsurf filmed, at 5:05 PM on the day of the Notre-Dame fire, a figure on top of the cathedral’s roof, as well as a flash of light. The scaffolding company said that its employees were on the roof until 5:20 PM.
You asked a question about the origin of a video posted by the French identitarian activist Damien Rieu, as well as many other accounts on Twitter. It is a video of low quality of the roof of the Notre-Dame cathedral in Paris. At the seconds 8 and 23, you can see white dots, that seem like sparks.
#NotreDamedeParis : cette vidéo ni datée ni authentifiée circule sur les réseaux sociaux.— Damien Rieu (@DamienRieu) April 17, 2019
Elle serait issue d’une webcam.
Voilà du boulot pour les fact-checker @decodeurs ou @CheckNewsfr @LibeDesintox 👀 (via KrocBlanc) pic.twitter.com/Mb3dmCiJs5
CheckNews found the video, fueling many speculations and posted on Reddit. Someone who posted the video on YouTube said that he recorded it from the website Viewsurf, and that it was shot on April 15 at 5:05 PM.
Viewsurf is a French website showing the streams of different public webcams in France. One of these streams is a camera filming the Notre-Dame cathedral, publishing a one minute video every hour.
Videos from April 15 are not online on the Viewsurf website anymore, however CheckNews was able to access to videos shot at 2:05, 3:05, 4:05, 5:05, 6:05 and 7:05 on the day of the fire. The 5:05 video also was saved on Archive.org. It is indeed the video circulating on social media.
You can see a figure moving on the cathedral’s roof on the 5:05 video. But it is also the case for every shot between 2 and 5, where you can see several people around the spire. No one is visible at 6:05. At 7:05, we couldn’t see anything but flames and a lot of smoke.
CheckNews reached out to the crisis spokesperson hired by Europe Échafaudage, the company in charge of the scaffolding on top of Notre-Dame's roof. They said that 12 people were working on the set up of the scaffolding. "the last worker who left the site did so after the electricity was shut of at 5:50. They left the roof around 5:20". In all likelihood, the figures seen on the video are workers hired by Europe Échafaudage.
About the light seen on the 5:05 video: we were able to see similar flashes on other videos during the day (at 3 and 4:05). These lights seem to be reflections, even though we cannot say that in certainty.