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60fps Slow Motion Calculations
Hi, guys, let’s talk about slow motion.
Are there any particular ways of slowing down 60fps footage that are better/smoother than others? How does the shutter speed influence that?
I need to know this cause I’m planning to shoot a music video for a band, and I want to do an effect similar to Coldplay’s “Yellow” video (https://www.youtube.com/watch?v=yKNxeF4KMsY), in which the singer seems to be moving in slow motion but still singing in perfect sync with the song.
To do this, obviously, you need to shoot with the song sped up so it syncs up to its actual speed when the speed of the footage is reduced.
So it has to be pre-planned: I need to know in what speed I need to have the song playing during the shooting. So I’m wondering if there are particular combinations of speed reduction and shutter speed to 60fps footage in order to get a nice, smooth video.
I want the final footage to be 24 fps for a film-quality, but do I actually need to reduce the 60 fps footage to that framerate? I think it’d be too slow for what we’re going for in the video (I can’t imagine going down further than 50% speed). And I guess 125 would be the standard shutter speed to shoot 60fps, but maybe there’s a better speed I can use in relation to the final fps?
I hope that was all clear, and if anyone can help, I’d really appreciate it.
Luis
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3 Replies
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You already have the idea, it seems.
For this video: https://youtu.be/EPTWR_7_xgA (not my video, but a friend’s)
Sped up the audio 2x and played back at 2x for the musicians to lip synch to during production, shot at 60p, then re-timed to 30p and dropped it into a 30p timeline with the original recording. If you are going to 24p from 60p (40% of original frame rate), retime the audio to 2.5x normal speed (24 x 2.5 = 60) then play back at 2.5x for the actors or whomever during the shoot and shoot at 60p, then retime the footage (don’t discard frames) to 24p instead of the original 60p. Remember to convert 60i to 60p before you retime footage. You can do all the retiming in Cinema Tools if you have it or even MPEG Streamclip I’m told.
Save early. Save often.
Jonathan Ziegler
http://www.electrictiger.com
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Thanks for the reply, Jonathan.
Retiming basically the same thing as telling Premiere Pro to “Interpret Footage” as 24fps, right?
The problem with that is it would be pretty much impossible for the band to convincingly play the song at 2.5x the speed (not even 2x, really). I was hoping to only speed it up about 30-40%, but I’m guessing that would result in discarded frames?
I mean, I could either throw the 60p footage straight into the 24fps timeline and then bring the speed down to 60-70%, or… interpret the footage as 24fps (which would make it play at 40% the original speed), and then speed up the video to the equivalent of 60-70%.
Would either of these methods produce acceptable results?
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You can shoot it how you want of course.
2-2.5x isn’t really that fast (depends on the BPM of the original, anyway) and they can fake the instruments due to the visual effect – people will want to watch the singer anyway. Shoot in small bursts – most musicians and singers can sustain a faster rate with the original track playing at 2-2.5x speed (pre-recorded of course) for small bursts pretty easily. Play it for them a couple times and have them go along with the audio. They’ll get it. Sometimes the singer cues get missed, but then you just keep rolling, have them go back a little bit, then do it again. Later on, shoot some fun/funky b-roll that you can cut to to keep the video interesting.
I find trying to convert footage on the time line correctly to be spotty at best and if you don’t do anything with the audio you’d have to drop frames in order for the “slo mo” effect to work. If you just want to slow it a little bit, shoot at 60fps then plan to go up the same proportion for the audio. It’s sooooo much easier to match these up first during production than trying to fiddle with it in your editor. Also, try a couple different methods to see which is best for you.
Save early. Save often.
Jonathan Ziegler
http://www.electrictiger.com
520-360-8293
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