Smooth Slow Motion

Hi -
I shot some footage 720p60 with my panasonic HVX200 -But when I slow it down to 20% or even 10% it's not smooth. The scenes don't even have that much movement. It's just people's faces smiling.

Is there a way to make the slow motion smooth?

Not really. You can try using Motion (or Shake, if you prefer) to do an optical-flow retime, but it's just inherently difficult to get good results when you do such a slight speed change as ten or twenty percent. The best results when shooting off-speed come from an integer speed change, such that one frame of source footage corresponds to one frame in your timeline. For instance, you could stretch that 720p60 material out to 250 percent and drop it in a 720p24 timeline; in that case you'd play back every frame of the 60p stuff, but at a slower frame rate. As long as you were shooting with a 180° shutter ? that's 1/120th, for 60p ? it would look perfect.

You could also stretch the same material to 125% and play it back at 24p; that would drop every other frame of the 60p source, which have the net result of turning your 180° shutter into a 90° shutter and thus would look a bit strobey, but you could maybe get away with it.

I just opened the footage in motion and applied the Optical Flow. It worked like a charm.
It would be great to have this feature right inside FPC. this was if all your clips in your timeline have SlowMo, you don't have to keep going back and forth between apps and adjusting timing on your FCP Timeline.

thanks Jeff

Good feature request Jeff.
Optical Flow works even better in Motion 4.
In Motion 3, it analyzed the entire media file, which was bad for people that capture tape rolls.
In Motion 4, it just analyzes the clip in the timeline.

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Does optical flow still produce that weird watery effect surrounding moving objects?

Does anyone know what I mean?

Harry

I've never heard it described that way, but I think I know what you mean, Harry. The answer is basically yes. Optical flow is a very clever, very good way of coming up with "in-between" frames, but it's still an interpolation. I'm sure others disagree, but I've never actually run into a situation where optical flow retiming was good enough to use in a client project.

That's a drag - I mean that they haven't fixed optical flow - because I agree with Jeff, it's really unusable insofar as it draws attention to itself with that weird halo surrounding moving objects. At least that's my experience.


Harry

"Fixed optical flow?" Optical flow isn't broken. Retiming is just one tiny application of optical flow technology. Optical flow is at the heart of 2D tracking, motion estimation for video compression, machine-assisted roto and all sorts of other things. And with optical flow, you can get better retiming than is possible with any other technique short of actually overcranking the camera.

What do you want, man? Magic?

Oh dear. Have I upset you?

I had no idea that Optical Flow is, as you say, at the heart of all these applications. Forgive my senseless blunder.

I was specifically referring to the only use I have ever had for this function which was to attempt to do a really smooth slow motion with interpolated frames, as advertised.

I found that, although it did all that interpolation stuff really well, there was a side effect present wherein the subject being slowed down (and this was a shot of a person running against a bright white snowy background) was surrounded by aura similar to ripples in a pond - or perhaps a heat shimmer.

Poetic, but ...

That was not what I had in mind when I applied this optical flow gizmo. I was expecting interpolated frames only.

Had I wanted a glowing ripple effect, I would, of course, have reached for the "glowing ripple effect" plug in which is available from Nattress free of charge, except on Thursdays when it costs $78,000.

Hugs,

Harry.

PS. I haven't tried it in Motion 4 and Kevin is suggesting that it "works even better in Motion 4".

So I'd better make another attempt.

H.

Sorry, I didn't mean to be snippy. The use of words like "broken" or "fixed" in contexts where they're not appropriate is one of my major pet peeves. The people who indulge in that are usually completely unaware of the big picture, and it gets on my nerves. I know that's not the case here.

Of course optical flow can't produce perfect results in every instance. Like I said before, I've never actually been in a production situation where optical flow worked for me. Part of that is because I've only had to do non-integer retiming maybe three or four times in my career, fortunately.

Regarding your PS, to the best of my knowledge the optical flow algorithm hasn't changed a bit since the Shake days. It's the same in Motion 3 and 4. It's just that in Motion 3, the whole clip gets analyzed, which takes a lot of processing time. In Motion 4, only the part of your clip between the in and out points get analyzed, so it's faster.

Hi Harry.

what "works better" in Motion 4 is it doesn't try to analyze the entire clip.
it's a house-keeping improvement.
the effect is the same.


*some* shots will respond ok,
but many wont.
one major problem is when you have a fg object moving against a bg.
it gets very confused trying to work that out.

i have used it, but have then had to spend a fair bit of time fixing the problems.
got good results in the end.

Andreas Keil suggested a method where he roto'd out the fg figure,
and did separate "optical flow" passes on the fg and bg elements,
before re-combining.


cheers,
nick