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Black Frame Flashes on Export with Alphas

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Matt BenepeBlack Frame Flashes on Export with Alphas
by on May 7, 2010 at 4:00:31 pm

So it looks like this has been asked numerous times, with no answers. That said, it hasn't been asked for awhile so maybe there's a solution now.

I've keyed out green screen on about 200 clips, and on export there are random black flash frames that show up. They sometimes appear when re rendering, and sometimes they don't (more often than not they still do). This has effected about 80 % of the files at this point and was looking for some reason it's happening and how to fix it.

Footage was shot HD, and dropped onto drive at 1920 x 1080 Apple Pro Res HQ. I went through and pulled takes, and exported through compressor. Exported clips out as 1920 x 1080 Animation (alphas were turned on during export, but we've experimented with having them correctly turned off on export to no avail). At this point they were pulled into AF, keyed and exported back out at 1280 x 720 Animations with pre multiplied alphas.


I've got a decent handle on this stuff, and the person helping with it is very knowledgeable, and both of us are left scratching our heads.

Does anyone has suggestions....or solutions would be even better! Thanks!


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Dave LaRondeRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 4:16:59 pm

[Matt Benepe] "So it looks like this has been asked numerous times, with no answers. "

Oh, it has, too -- in fact, if the cause is what I suspect, this is the second time today, and it's still morning. You need to look harder.



[Matt Benepe] "Footage was shot HD, and dropped onto drive at 1920 x 1080 Apple Pro Res HQ. I went through and pulled takes, and exported through compressor. Exported clips out as 1920 x 1080 Animation (alphas were turned on during export, but we've experimented with having them correctly turned off on export to no avail)."

What? You tried exporting clips as if they had alpha channels, even though you hadn't done anything to them to change their opacity? That's weird, not to say unnecessary. At least you're not working in a long-gop codec.

But there are still three VERY common causes of AE weirdness you need to check:
Got the free upgrade to AE 9.0.2? Get it.
Trying to use Open GL to accelerate renders? Don't: turn it off.
Trying to use multiprocessing with insufficient RAM, i.e. 6GB or less? Turn off multiprocessing

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Tudor "Ted" JelescuRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 4:42:22 pm

Dave is right- also, why export from AE with alpha? AE is a compositing program and you should do the compositing in there where you have a lot more control and then export the final piece without need for alpha.

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


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Matt BenepeRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 5:53:49 pm

Dave, thanks for editing your original response.

Back to the question at hand, from the delivered source files they were Pro Res HD. That's what it says when I did what you asked. They were shot on a EX-3 4:2:2 1080p, and again from the production company "Pro Res HD codec"

I'll try checking the things you suggested. Yes, I didn't need to export the original files out of FC with Alpha's since there wasn't any, but I do need to keep the alpha channels from AF.


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Dave LaRondeRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 6:14:24 pm

[Matt Benepe] "Dave, thanks for editing your original response. "

Hey, I was dead wrong. Upon re-reading your original post, I gave myself a dope slap. I thank you for your self-restraint in not flaming me for failing to do my job properly, which involves reading for understanding.



[Matt Benepe] "They were shot on a EX-3 4:2:2 1080p, and again from the production company "Pro Res HD codec" "

Okay, watch out for footage that originates in any XDCam. It's long-gop, and very bad for AE.

I presume you also have FCP 7 installed on your AE machine, or you wouldn't have the codec and couldn't see the images.

I also presume you've inspected the codec of the clips imported into AE to confirm that they are NOT in native XDCam acquisition codec, but are in fact in ProRes HQ.
Incidentally, ProRes HQ is overkill for XDCam footage: you get NO improvement in image quality, just unnecessarily-large files. Got some RED footage at 2K or 3K? ProRes HQ is the way to go.

I still smell a codec rat because your symptoms are precisely those of having the wrong kind of footage in AE. That's why I'm banging away on double-checking codecs. Start there first.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Matt BenepeRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 6:27:35 pm

The original files were exported out from FC as Animation codec after clip selection. Those were pulled into AF for keying. After keying they were re-exported as animation, and resized form 1920 x 1080 to 1280 x 720 with an pre multipled alpha channel.

I'm working on these clips as well as an outsourced guy that is working off of a PC with AF. Since he's helping Key, he's getting only Animation codec files

The source files are not xd cam, and are Pro Res HQ.


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Dave LaRondeRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 6:46:21 pm

Well then, those clips may be okay. Give the guy a test clip and see if it works. If you don't have something like a RAID 5, Animation clips can't play back in real time: they play on most machines in fits & starts.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Dave LaRondeRe: Black Frame Flashes on Export with Alphas
by on May 7, 2010 at 7:16:30 pm

Another thing to check: FCP defaults to preferring straight rather than premultiplied alpha channels. You made premultiplied chips. How 'bout a test clip in a straight alpha channel, too?

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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