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Using AE and keylighting and getting a flickering problem

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melissa leUsing AE and keylighting and getting a flickering problem
by on May 3, 2010 at 12:27:23 am

Hi,

So, I made a composition and I placed a video of my friend in it. He has a green screened background behind him so I green-screened it out using Keylight 2.0. I placed a mask too around the video so I wouldn't have to use the whole footage as well.

Then I placed that composition into my final composition. (It's a 3d composition. does that matter?)

Everything looks fine until I press render. I rendered my footage and in the end I ended up getting some "bad frames." For some reason my video of my friend that was green-screened out keeps flickering black randomly. I have no idea why. I checked all the frames per seconds settings and they're all identical.

Any suggestions?


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Bret WilliamsRe: Using AE and keylighting and getting a flickering problem
by on May 3, 2010 at 3:10:58 am

I have this problem at times. If two items in a 3D comp are VERY close in z space, then often AE thinks that one is behid the other for a frame or two depending on where the camera is. It's just plain wrong and one of the few truly nasty bugs in AE. All you can do is make sure there is some definitive space between the 2 layers. Usually a half pixel or pixel of depth will do. If one is at z=0 then make the foreground element z=-1. Sometimes I've had to bring them forward so many pixels that it compromises my design and I figure something else is going on, but the comps can be so complex I just work around it.


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Tudor "Ted" JelescuRe: Using AE and keylighting and getting a flickering problem
by on May 3, 2010 at 10:24:24 am

Also, if you have 2d layers in between the 3d layers, there can be glitches.
I think that your problem may come from the compression of your initial footage. If you got footage with any sort of compression (DV, mpeg...)you need to render that out to an uncompressed version and then pull the key ( take out the green screen).
Dave LaRonde has some great advice for this:
"Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, AVCHD, mp4, mts, 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. "


Tudor "Ted" Jelescu
Senior VFX Artist
Bucharest, Romania
http://www.ennstudio.ro


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melissa leRe: Using AE and keylighting and getting a flickering problem
by on May 4, 2010 at 8:14:09 pm

the original footage that was green-screened is just a typical .avi file. I changed it to .mov but that didn't do any changes too.


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melissa leRe: Using AE and keylighting and getting a flickering problem
by on May 4, 2010 at 8:12:43 pm

I tried this and worked find when I was previewing it. But when I clicked "make movie" and after 30 minutes of rendering my 3 minute video I checked it out again and it was epic fail. Everything still blinked.


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Dave LaRondeRe: Using AE and keylighting and getting a flickering problem
by on May 4, 2010 at 10:08:25 pm

What kind of footage did you shoot for the chroma key? It makes a big difference:

Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, AVCHD, mp4, mts, 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
KCRG-TV (ABC) Cedar Rapids, IA


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Tudor "Ted" JelescuRe: Using AE and keylighting and getting a flickering problem
by on May 5, 2010 at 8:37:16 am

Try rendering out tiff or tga sequences and then pull the key.
If that does not work, it may be that you need to play with the edges of your matte.

Tudor "Ted" Jelescu
Senior VFX Artist
Bucharest, Romania
http://www.ennstudio.ro


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