Frame rates for speeding up video in post

[Straker]

Hi, I'm going to be shooting video with the intent of speeding it up for the final cut.
It's for a music video, and we will be shooting the band playing along with the song at 40% speed.
The final video will sped up to bring the 40% speed to match the soundrack at 100%
The question I have is your suggested framerates for shooting 4k and/or 2.5k with the intent of speeding it up x 2.5, also anything else to consider.

This will all be shot following a smallish boat cruising at low speed.

Thanks!

 

[zocalo]

In general when doing any speedup of video like this the easiest option is usually to stick with multiples so that all the editing suite has to do is adjust the frame rate and/or drop frames, and ideally every n'th frame. Shooting at less than 50% of the final output speed also means you can shoot at a slower frame rate giving you less data to process and still get 50/60fps output.

In your specific case it's really easy: just shoot at 24fps, then just adjust the playback rate to 60fps; that's an instant change from 40% to the required speed of 100% (40% of 60 is 24). If you want a different output frame rate than 60fps, e.g. 50fps, then dropping every 6th frame to achieve that is trivial for any editing suite and won't introduce any significant additional artifacts.

 

[brett8883]

In general when doing any speedup of video like this the easiest option is usually to stick with multiples so that all the editing suite has to do is adjust the frame rate and/or drop frames, and ideally every n'th frame. Shooting at less than 50% of the final output speed also means you can shoot at a slower frame rate giving you less data to process and still get 50/60fps output.

In your specific case it's really easy: just shoot at 24fps, then just adjust the playback rate to 60fps; that's an instant change from 40% to the required speed of 100% (40% of 60 is 24). If you want a different output frame rate than 60fps, e.g. 50fps, then dropping every 6th frame to achieve that is trivial for any editing suite and won't introduce any significant additional artifacts.

Yea this ☝☝is correct and a very good understanding of how frame rate and playback speed go together. Rarely does it work out so well like this.