Resolve default handling of mixed frame rates
The default “Resolve” handling of mixed frame rates is to discard or duplicate frames and keep the same length as the original. This is OK when the source is 50 fps, and you add it to a 25 fps project. Every other frame is discarded, and motion is smooth. The same is 60 fps in 30 fps.
Many film festivals will be able to screen 30 FPS DCPs instead of 24 FPS DCPs, so you could make both a preferred 30 FPS DCP and a backup 24 FPS DCP to avoid discarding.
Discarded and duplicated frames
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. For a 24 FPS film in a 25 FPS project one frame each second is duplicated. 23.98 FPS films in 24 FPS projects will also be adjusted.
Avoiding adding or discarding frames
You can change Resolve mixed frame rates setting not to discard or add frames and instead change sound speed. This is used when converting 25 to 24 or 23.98 to 24.
In Project setting – General options
Change Mixed frame rate format from Resolve to None