Just a brief bit about me - i'm a novice videographer who has gained all of my knowledge from the internet. I shoot a lot of music video's and recently purchased myself a Lumix GH4.
Now for a long time i was making the mistake of editing all of my video's on a 60p timeline which at the time worked well. After doing some research on the correct workflow i've switched over to a 24p timeline. I recently done some filming in Bath in which all of the b-roll clips i was very careful to film in 60fps at 120 shutter speed. From what i understand this is the correct procedure if you plan to slow clips down smoothly.
So i've now put the clip into the 24p timeline, hit automatic speed which takes it to 40% and also used the optical flow.
For what reason is the slow-motion still slightly choppy? What am i missing out in this process?
If you are shooting at 24 fps, be sure to use 1/48 or 1/50 shutter speed to give the appropriate motion blur. I see a lot of sports shot on DSLRs where this is ignored and it gives a very choppy look. I film lacrosse and prefer to use 60 fps and then for clips that I slowdown, typically to 50 % the slow motion looks great.
Sorry maybe i haven't made this completely clear. I'm filming for a music video. So i've shot all of the performance shots at 24FPS and all of the B-roll at 60FPS. I'm then editing it onto a 24p timeline in the hope of slowing all the B-roll down to 40% with it still being smooth.
For what reason is the b-roll still choppy after following the correct procedures including shooting at 1/120 shutter speed?
I don't know the technical thing behind this but I believe that it is choppy if you don't match the shooting fps and the edit fps. It's easier to understand when you film at 24 fps and you edit in 30fps. The software has to 'add' 6 frames. So when you want to edit 24 fps. You have to film 24fps or 48 or 96 for a smooth playback.
Once I had to solve it and I converted the footage in Adobe media-enoder. I had to make 1 important adjustment in the settings. It was something like 'dissolve between frames'. (I am not home to check the exact settings). So you can try to convert a piece of the slowmo-footage to 48 fps in Media Encoder and try different settings.
[Michiel de Leeuw van Weenen]"I don't know the technical thing behind this but I believe that it is choppy if you don't match the shooting fps and the edit fps. "
If you play back the frames 1:1 the only "choppiness" is going to be from shutter speed or not enough frames, and perhaps flicker from an errant light source.
You can record any frame rate and play them back at 24 or 25 or 30 and there is no interpolation. Each playback frame rate will result in a slightly different speed. There is no reason to interpolate frames if you are planning to playback 1:1. If shot at 60fps, playing back at 24fps is going to give about a 60% reduction in speed. If you playback at 30, it will be a 50% reduction in speed (resulting in slightly faster motion as there's more fps to playback).
Liam, is there anyway you can post a little bit of the footage?
Like the others, I can't quite understand why Final Cut is getting you to apply optical flow if you're playing back 1:1. Where are you applying the optical flow - In the retiming menu or using the rate conform option in the info pane? Can you choose to not apply any interpolation? it shouldn't need it.
Just an aside, if you go into the GH4 options and set it to use shutter angle instead of shutter speed, you can just set it to 180 degrees and the shutter speed will always be correct no matter what fps you've set. Just gives you one less thing to think about in the middle of a shoot.
Jeff Kirkland | Video Producer & Cinematographer
Hobart, Tasmania | Twitter: @jeffkirkland