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Weird shuddering effect using Twixtor

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Ed Moore
Weird shuddering effect using Twixtor
on Jun 29, 2007 at 11:20:46 pm

Hi there,

Just bought Twixtor and FieldsKit today. Having a lot of fun but keep coming up against the same weird visual effect when trying to create slow motion shots. I'm not sure whether I'm just being over-ambitious, or if I have something set up wrong.

You can see an example of the end product at http://www.fullrange.co.uk/stirry_twixtor.mov (900KB H264 QT).

What I'm describing is how, rather than one fluid speed, the video appears to suddenly move a great deal, then settle for a moment, then suddenly forwards again.

The original footage is of a pan being shoved back and forwards with a very regular cadence so it definitely shouldn't look like this slowed down.

CURRENT WORKFLOW:

The original footage is 1080 50i HDV, shot with a 1/120 shutter speed.

1. Convert footage into Uncompressed 10bit 1080i 50
2. Take uncompressed footage into 16 bit After Effects 6.5 project
3. Create a 1080 50P sequence
4. Drop the uncompressed footage into the 50P sequence, add FieldKit
5. Set FieldKit to the "2XFPS" option, Upper field, and motion settings as best dealt with the interlacing

(at this point I can step through the 50 frames in each second of this sequence and they are definitely all different and nicely deinterlaced from the original 50i)

6. Create a new 25P sequence
7. Drop the 50P sequence in
8. Create a solid and apply Twixtor 4.5 to it
9. Set Twixtor's colour source to be the 50P sequence layer
10. Set Fields to Off
11. Set Input frames to 50
12. Set speed to 12.5
13. Set blending mode to Blend
14. Render without fields

Where am I going wrong?

Many, many thanks for any light you can shed!

Regards,

Ed Moore



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Pierre Jasmin
Re: Weird shuddering effect using Twixtor
on Jun 30, 2007 at 1:31:17 am


6. Create a new 25P sequence
* You mean set comp setting to be 25 FPS

7. Drop the 50P sequence in it
8. Create a solid and apply Twixtor 4.5 to it

* Note you would also have the option of doubling the first comp duration (in it's comp setting) and then drop that into the new comp and apply Twixtor directly to that

9. Set Twixtor's colour source to be the 50P sequence layer
10. Set Fields to Off
11. Set Input frames to 50
12. Set speed to 12.5
13. Set blending mode to Blend
14. Render without fields

* Aside from that what you say looks OK at first glance. However as per your result there seems to definitively be somewhere a "source time" field reversal issue which causes the slowmo bounce you see. Any way you can send a 10 frames sequence with your AE project to techsupport@revisionfx.com so we can look at it step by step.

Pierre
RE:Vision Effects



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Jeremy Mullen
Re: Weird shuddering effect using Twixtor
on Dec 15, 2008 at 4:29:02 pm

I'm wondering if there's an answer to this problem - I'm having the exact same thing happen to footage I'm trying to run very slow. Can you guys bring an update to the Cow? Thanks!


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Pierre Jasmin
Re: Weird shuddering effect using Twixtor
on Dec 15, 2008 at 5:08:19 pm

It's hard to evaluate what your issue is without seeing your project
(a project to techsupport at revisionfx dot com would help)

Pierre



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Ed Moore
Re: Weird shuddering effect using Twixtor
on Dec 15, 2008 at 7:56:59 pm

Jeremy - if you have After Effects CS3 I suggest you use the Pixel motion mode which produces similar results to Twixtor (without this issue).

Pierre - *I* sent you my After Effects project on 30th May 2007 with a clear example of the same issue. Still looking forward to your reply! :)



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Pierre Jasmin
Re: Weird shuddering effect using Twixtor
on Dec 15, 2008 at 8:11:46 pm


Ed,

I did request 10 frames from you to look at and as per above message on this thread, but I just checked and I did not get anything from you yet :)

His problem is not necessarily yours, is often an FPS setting, either the FPS value in Twixtor does not match the FPS of the comp (or the FPS was set manually e.g. 29.97 while it's actually 29.97002997002997...). This might seem like a little difference but 29.97002997002997 (30000/1001) is what FCP, Premiere or Avid exports (and typically it would show in AE UI as 29.970 -- note the last 0) - and that tiny difference can cause frame rounding errors. In fact I remember testing CS2 -> render 29.97 FPS with fields in AE, load in Premiere and rerender 29.97, load back in AE and drop into a 59.94 comp... and half the fields were gone. That tiny difference just happens to make the second field fall in the 0 to 0.5 time interval of the first field...

Pierre



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Peter Litwinowicz
Re: Weird shuddering effect using Twixtor
on Dec 15, 2008 at 11:07:59 pm

Thanks for sending the project + footage.

There are two problems:

1) One problem is that you are working in less than 100% resolution for your main comp.
There is a way around this:
Make sure when you import your footage that the AE’s Interpret Footage->Separate Fields is set to Upper.
Set AE to work at 100% resolution (and make sure to set resolution AE is using to actually calculate the images... Not the viewing display resolution).

2) It looks like getting random frames from the HDV codec you are using causes AE to go a bit crazy and will not allow us to get the frames/fields properly. So you are doing nothing wrong. It is just that AE and HDV do not play nicely together.

Here is a “Creative Cow” forum post, by someone who really knows these issues: http://forums.creativecow.net/readpost/2/942432

The main info is this:

Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- Native HDV, MPEG1, MPEG2, mp4, m2t, H.261 or H.264 -- you need to convert it to a different codec.

These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.

In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.

Dave LaRonde
Sr. Promotion Producer

You are using one of the formats AE does not play nice with, so you’ll need to recompress to another format before trying what you are trying in AE.

Pete




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Jeremy Mullen
Re: Weird shuddering effect using Twixtor
on Dec 18, 2008 at 2:05:36 am

Thanks all for weighing in. I kept fiddling with the figures and going through the tutorials and manuals again and again, until I came to the conclusion that my main problem was trying to slow down excessively fast motion too much. When I pushed the vectors up, I could see the plugin working all liquidy in there (apologies to S Palin), but there wasn't any real image info to be had. I still got this kind of pulsing action - the motion moves forward, and stops, and moves forward and stops - but write this off to an optical illusion based on lack of pixel information where Twixtor is 'tweening'.

I do still have one question, though - my footage is undeniably 30 fps, progressive, DV/NTSC; for whateer reason, I like the results Twixtor gives me in super-slo mo when I set its frame rate input to 15 fps. Why would that be? Is it my imagination, or does that smooth out the super-slo mo a little more?


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Pierre Jasmin
Re: Weird shuddering effect using Twixtor
on Dec 18, 2008 at 4:01:21 am

" I like the results Twixtor gives me in super-slo mo when I set its frame rate input to 15 fps"

If you set "Input Frame Rate" in Twixtor to 15 and your comp is 30 FPS, then what happens is that Twixtor will skip in source time space half the frames,

That is if you have frames 1,2,3,4,5,6,7,... and 50% slowdown
Twixtor will make inbetweens using frames 1 and 3, then 3 and 5,... rather then 1 and 2, then 2 to 3, then 3 to 4...



Pierre




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