Slow motion on FCPX - Problem!

Hello everyone!

Well I was testing to see if I could do a Slow Motion video on FCPX but I'm having some problems.

I've seen different tutorials on this subject and they are based on:

1) Slow the video to 25%, 10% or other rate;
2) Choose "Optical flow" on video quality

I've done this and I've also tried the other method which is to first convert the original video to Apple Pro Res 442 with the MPEG Streamclip app but it's the same.

My problem is that the slow motion adds a weird effect on the video.

Here is the test I made:




First I tried with 10% slow motion with Optical Flow and then at 10% with Frame bleding, but it looks bad!

The video was shot with a Canon 600D at 25 fps.

Does anyone know why this is happening and what can I do to make a decent slow motion effect?

Thank you all in advance!

It's probably to do with your original frame-rate. That might be the best you can get at 25fps.

Maybe try shooting the same thing again at 60fps, or higher if your camera can.

Some claim the Twixtor plugin produces better slomo, but with your initial frame-rate so low, there's only so much magic that can be done.

Here's the math. You're slowing down a 25fps clip to 10% of its original speed. So you're trying to fill every 1 second of video with 2.5 frames, that you would normally be using 25 frames for. You're asking too much of your source footage. If you used 60fps instead of 25fps, you'd have 6 frames every second as opposed to 2.5 frames. You'd have over twice the number of frames to work with. This is why you shoot in a higher frame rate for slow motion. There's only so much you can do with your normal framerate.

Try easing up on the amount you're slowing the clip down. Try 40 or 50%. It will look much better. It won't be as slow, but it will definitely look better.

You could try Twixtor, since it's what it was really made for. Just don't expect perfect results.

Shoot at 60fps, edit that inside of a 24/25fps timeline. Use the Conform command in the retiming menu on it. You'll get in-camera 40% slow motion to start with, no faked frames. Then slow that down and your even slower motion will be much better.
Here are some illustrations of how it works.

For optical flow, just misc fyi, also be sure there is little to no motion in the background of your clip, as that can throw it off.

Hello, thank you all for the explanations!

I will try to do some footage at 60fps and I'll let you know how it went. And I'm gonna try that Twixtor.

But now that I'm looking for other Canon 600D slow motion movies, most of them have the same problem that I have, even with 60 fps, although it's not so visible.

Without knowing the exact process the other Canon 600D editors used to create the slowmo from their 60fps footage, don't write your camera off yet.

Since 60fps at 720p is the highest rate your camera is capable of, first try exactly what Ben described. Utilizing FCPX's full capabilities before you pass judgement. It may just be enough magic to override your perceived problem.

Worth a try...

A member of my FCP users group does a lot of BMX stuff, does the 60fps conformed to 24fps technique all the time. Then slows it all WAY, WAY, WAY down with Optical Flow. His results are super impressive.

Here is an example of what he can achieve with this technique.
vimeo.com/41117635

BenB wrote: … does the 60fps conformed to 24fps technique all the time. Then slows it all WAY, WAY, WAY down with Optical Flow. …

blame me stupid, but does it make a difference:

conform (e.g. 60fps recording >>30fps timeline) + slowing down 50%

or
slowing down 60fps recording in a 30fps timeline by 25% ?


in other words:
is FCPX clever enough to use 'underlying' frames?
Or, by conform speed, do I have to tell it 'manually'?

Hi Karsten,

Not stupid at all, it's a very good remark.

Yes, it will make a difference.

FCP X, as any other NLE, assumes by default that you want all video on your timeline to run at “normal” speed. When it detects clips on your timeline that have a different frame rate than your Project frame rate it will add or remove frames automatically to compensate for this difference so that the speed of action (the duration) of your clips always stays at 100%. So how does this relate to extreme slow motion?

1. Slow motion without conforming

When you drop a 50p clip on a 25p timeline FCPX will by default drop every other frame to make your 50p clip play at 100% in your 25p timeline.

When you slow down this clip FCPX will add duplicate frames to every frame it sees on the timeline to make the clip play slower. This means it will NOT use the original 50 frames, only the 25 frames that are left on the timeline. The more you slow down the video, the more duplicate (fake) frames will have to be added.

Duplicating frames, even using advanced frame blending or a dedicated algorithm like Optical Flow, can result in visual artifacts or choppy motion. It very much depends on how well the video was shot and especially how the slowed down action foreground relates to the background. If the background is stable or static and the action is very distinct optical flow can do wonders. If the background moves too much or the action foreground blends too much with the background the results can be ugly, no matter what algorithm or software you are using.

2. Slow motion with conforming

When you drop a 50p clip on a 25p timeline and you use the Conform command FCPX will preserve every frame of your 50p clip and spread them over the 25p timeline resulting in 50% slow motion. As no duplicate frames are created in this process this slow motion will be extremely smooth. Only when you want to slow the action beyond 50% will FCPX add duplicated frames. But as you have 50 clear frames on the timeline to start with and your video is already perfectly slowed down to 50% you will be able to get much cleaner results when you push the slomo far beyond 50%.

The video Ben has posted is indeed an excellent example of this. The action foreground is distinct from the background, the cam is locked so there is no movement in the background, and the video was shot at a higher frame rate than the project frame rate. An ideal starting point for achieving a great slomo using optical flow.

a big DANKE, Ronny for your in-depth reply!

.... and boom! my version of FCPX has a new keyboard-short-cut
(found out lately how to do my own layouts), ....

ctrl-shift-G

G stands for Geschwindigkeit anpassen / conform speed
and, usually, before applying slow-mo, I like to detach audio, which is ctrl-shift-S
I like to keep the original audio-speed while my lil' soccer-kickers move slooooow :lol:

thanks again!

for your slowmotion to be better you need to shoot at a higher frame rate and a higher shutter speed, this is what works for me, 60 Frames per second @ 720p ( since canon's doesn't have 60fps at 1080 ) and bump up the shutter to 1000-4000, test out different shoots to see what you prefer

Hope this helps!

Did I mention this article about slo-mo in FCP X? It has illustrations.

KingAhSing wrote: for your slowmotion to be better you need to shoot at a higher frame rate and a higher shutter speed, …

my projects (wow, big word! filming my son's soccer team ....) are 720/25p, and lucky me, my main cam shoots 1080/50p, and two, really cheap ones, used un-manned, in 720/60p.

so, re-framing ("was it a foul, really?") and the 'base' for slowmo is laid.

I just thought/hoped, FCPX grabs all data automatically.
but now, with my new keyboard shortcut, it's fast AND beautiful.

again, thanks to all for your support!