American filmmaker Rian Craig Johnson tweets the following regarding the 1917 movie in his twitter account.
Last night at the PGA awards Mendes told me 1917 was ACTUALLY shot in one continuous take, if an actor flubbed a line they’d go all the way back and start again from the beginning. They paid Cumberbatch to show up every day and wait in that room at ...
Most of the movie is filmed with 8-9 minutes long scenes and then edited to make it look as a continuous shot. Sometimes they pass the camera behind some objects (I remember some rocks and buildings) and cut the scene, then they can continue with the next scene without the audience noticing the cut.
There's an article with most of the process explained.
Similar techniques were used in Birdman which was also visualised as a single shot, and the opening scene of The Revenant.
Usually, if you're looking out for them you can see the wipes they use - watch for someone crossing camera in such a way as they completely cover the shot, or in Birdman, they used transitions between rooms, covered by CGI to keep the ...
Quoting from Wikipedia under filming section.
Filming was accomplished with long takes and elaborately choreographed moving camera shots to give the effect of one continuous take.
Careful editing was employed to trick the viewer’s eye into thinking they were watching films unfolding in one unbroken take. (source)
Sam Mendes explained it quite well ...