How to manage project with mixed frame rates?

I have a project with 25, 50 and 30 frames per second footage, all HD. I want my project to be output at 25FPS, what is the best way to handle/process the files at varying frame rates to ensure a smooth edit and output?

I also often have to create projects with various source of footage at different frame rates, varying from 25fps to 60fps.

To be honest, the results are not always good because frame-rate conversion is fraught with problems and will never be "perfect". If you use optical flow you can get some really obvious artifacts on some footage (although on other footage it can be quite good) and if you simply opt for frame-dropping then continuous motion can become noticeably jerky at times.

My previous NLE used to offer "resampling" when converting frame rates but it was worse than useless... tending to add huge amounts of motion-blur to everything.

Perhaps there is a "correct" way to handle this but I don't think one approach works every time.

Using 50fps footage on a 25fps timeline is easy -- dropping every second frame produces a nice fluid flow that is imperceptible. However, pulling 30fps footage down to 25 produces really bad results most of the time. One option I have used on occasion is to "stretch" the 30fps by changing the playback rate to 25fps with the clip retime option . This will make the footage play 16% slower but in some instances, this is not noticeable -- or at least it's not as noticeable as dropping frames or dealing with artifacts of optical flow processing. I wish the Fairlight tab offered the ability (does it and have I missed it) to stretch audio without changing the pitch -- that would make retiming 30fps to 25fps even better.

I second that. For anything but a full numbers ratios (like 60 to 30 or 50 to 25) the program will have to 'invent' frames that were never recorded in the first place. This can work sometimes, but it's a very content sensitive process, can look downright awful at other occasions.

Slowing 30 down to 25 (Clip Attributes) is the best solution. BTW, I'm not the audio guy, but my colleague showed me that Resolve can slow audio down without pitch change now, just look for it.

Thanks guys, I guess setting the project to 25fps and allowing the 50 fps footage to just drop every second frame (does it do that automatically?) and stretching the 30 fps may be the way to go.

Well here is an interesting result....

After experimenting with changing the frame rate of the 30fps files through attributes, to 25fps to match my project/timelilne settings and then dropping them on the time line, yes that works and yes the clip slows down as expected.

After I dropped a 50fps file on the timeline without changing its attributes and it played at correct speed, it got me thinking.

So I then dropped a 25fps, a 30fps and a 50 fps file onto the time line to see what would happen. Everything played back at correct speed and looked great, why I wondered.

I then output the timeline as a finished MP4 at 25fps to see what would happen. Much to my surprise, the output file was perfect. Somehow Resolve is changing the frame rate of the 30fps and 50fps files to 24 fps for output (and timeline playback for that matter) and the resulting video has no apparent jerkiness, totally smooth as butter.

Other applications I have used when doing this result in very jerky playback because the frame rate conversion is so bad, bravo Black Magic bravo!

It depends on the settings under Projects Settings > Master Settings > Frame Interpolation (all the way down).

"Nearest" can look jerky, "Frame Blend" can generate double contours on moving objects and "Optical Flow" can be the best, but may generate artifacts depending on image content and motion.

My settings were stock, so it was set to nearest and looks great, must be my lucky day!

Well, if you live in the US and are a bit older, you are used to 3:2 pulldown

What is desired output fps, 25?
25 and 50 is easy. Set nearest frame for 50 and Resolve should simply drop every frame for 50p sources.
25 and 30- this won't go well. Best solution is to convert 30 to 25 outside Resolve (open source, Alchemist, Tachyon). You can also try Resolve motion interpolated conversion, but depending on source nature result will vary.
Maybe I should setup some website for affordable conversion. Anyone interested?