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A 25 FPS film is the same length in a 24 FPS project and a 25 FPS project in Resolve. To achieve this, Resolve drops every 25th frame in the 24 FPS project.
(The same applies to 23.98 FPS films in 24 FPS projects)
Final Cut X and other video software change the film’s length instead and stretch the sound with phase sync.
Some ways to avoid frame dropping in Resolve
Convert the frame rate in Final Cut X and then import the converted film in Resolve.
Export only the sound from Final Cut X and change the frame rate on the video file in Resolve.
Change the frame rate on the film
In “Media bin,” right-click the film and choose “Clip Attributes,” Change it from 24 to 25. Resolve will now interpret the source file as 24 FPS even if it is 25 FPS.
Add the converted sound from Final Cut X. The film will be longer, but with no frame dropping.