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FLV w/ alpha channel -- weird white flashes

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Jason Metter
FLV w/ alpha channel -- weird white flashes
on May 15, 2009 at 11:35:36 pm

I am working with some video that was keyed reasonably well in AfterEffects using Keylight and output correctly (RGB+alpha, straight, etc.). I converted the MOVs to FLVs in Media Encoder, using On2VP6, checked Encode Alpha Channel, VBR bitrate encoding, etc.

The videos generally look okay, except for the portions the crossfade from 0% to 100% opacity. In these cases, they appear to fade from white instead of 0% opacity. So the effect is a white flash, instead of a gentle fade from transparent to opaque. Here is a sample of the problem area.

The rendered MOVs look fine. The problem seems to be occurring when converting them to FLVs. I've imported both into AfterEffects and the MOVs look good, but the FLVs have that weird white flash issue.

Any ideas on why this is happening and how to fix? Thanks in advance for your help.


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Justin P. Junda
Re: FLV w/ alpha channel -- weird white flashes
on May 19, 2009 at 1:07:23 am

List your setting for both the MOV output Animation setting, h2.64 etc... and list you FLV setting that you convert to. Are you converting using Flash or Adobe Media Encoder or something else?

Justin P. Junda


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Jason Metter
Re: FLV w/ alpha channel -- weird white flashes
on May 19, 2009 at 6:55:52 pm

Thanks, Justin. Here is more detail on my settings.

QuickTime rendered from After Effects:
Animation compressor, RGB+Alpha, Straight Matted

Converted to FLV in Media Encoder:
FLV, On2VP6, checked Encode Alpha Channel, 29.98fps (also tried 14.98fps), two pass VBR bitrate encoding (also tried one pass and CBR), 1500 kbps bitrate (will ultimately lower this).


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Justin P. Junda
Re: FLV w/ alpha channel -- weird white flashes
on May 20, 2009 at 7:38:51 pm

First of all, Ive seen weird things happen when people try to max out values like that lower that value. Second, it sounds like the transparency is never there. Well, that because its technically not. I missed it the first time in your post but the problem is that it needs to be premultiplied instead of straight in your settings also make sure you use millions of colors + with equals RGB +alpha, which you said you already do. Hope this helps any other questions let me know.

Justin P. Junda


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Jason Metter
Re: FLV w/ alpha channel -- weird white flashes
on May 20, 2009 at 7:58:07 pm

Transparency is present -- otherwise you'd see the green screen or some other background color around the person. I think "straight" is the way to go instead of "premultiplied," which is what I've done. And yes, as I've stated, I rendered at millions of colors/RGB + Alpha. Thanks though.


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Jan Lubeck
Re: FLV w/ alpha channel -- weird white flashes
on May 20, 2009 at 10:48:23 pm

Hi, sorry for highjacking this thread, but I found it looking for a solution for my own problem, and I think it might have something to do with what is happening to Jason.

My problem is that after converting the mov file to FLV with the alpha channel, the video gets very bright.

Here's an example to illustrate it: http://www.fyrastudio.com/jan/alpha_problem/

You can also find the original mov file there.
It was encoded with the Animation Codec, RGB+Alpha, Millions of Colors+, Premultiplied (Matted) Here it says that Flash only accepts Premultiplied alpha channels.

Anyway, anyone has any ideas? Sorry again Jason for using your thread, but maybe we can both benefit from this :D

Cheers!



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Justin P. Junda
Re: FLV w/ alpha channel -- weird white flashes
on May 21, 2009 at 2:22:20 pm

Jason I looked back maybe I wasnt clear about the transparency. I understand it has some transparency cause the green or whatever color is gone, however there are four color channel R, G, B, Alpha when it is straight the semi transparency blows out to white. You can use straight if you want its your project, but it doesn't hurt to try it and see if you get the result your looking for I bet you will. Straight floods any transparent pixel with white, so when yours transparent video starts to fade in it floods it with white giving the problem you speak of.

Jan this is also your same problem.

below is the link to a cow video that explains the two. Oh and Jan is right Flash wants a premultiplied vs straight. Just watch the video and your will see your exact problem.

http://library.creativecow.net/articles/rabinowitz_aharon/straight_vs_premu...



Justin P. Junda


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Jason Metter
Re: FLV w/ alpha channel -- weird white flashes
on May 21, 2009 at 4:14:53 pm

Thanks again, Justin. I don't think the video tutorial you linked to was necessarily recommending rendering out premultiplied for conversion to FLVs. I didn't hear any reference to FLVs or Flash actually. I went ahead and tried it anyway and I don't see any difference on the issue.

Take a look:
Premultiplied Sample
Straight Sample (same as original link)

I appreciate your help though.


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Justin P. Junda
Re: FLV w/ alpha channel -- weird white flashes
on May 21, 2009 at 7:25:26 pm

Can you send me this project file I guarantee I can get the result your looking for I'm very curious now. I know it didn't reference FLV but the concept of AE video exporting still follows the idea. Yoo can either post a link or send it to justinatjustinjundadotcom (apam prevention).

Justin P. Junda


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Jan Lubeck
Re: FLV w/ alpha channel -- weird white flashes
on May 21, 2009 at 7:35:59 pm

Hey Justin,

I saw your response to Jason, put my video was already encoded with the alpha premultiplied. So that doesn't do it for me. Any other ideas?

If you want to give it a try, you can download the mov file from the page I posted before. And the idea is simple, basically to have the colors on the right, with the transparency on the left, which I can accomplish with that same mov inside after effects for example.

Thanks for your help!


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Jason Metter
Re: FLV w/ alpha channel -- weird white flashes
on May 21, 2009 at 11:06:10 pm

I appreciate the offer, Justin. Here is a 17MB zipped file that includes an After Effects project file and a very short sample of a video file I'm working with. Just the relevant/problematic bit is in there -- a fade to transparent. Hope you can solve. Thanks again.


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Justin P. Junda
Re: FLV w/ alpha channel -- weird white flashes
on May 26, 2009 at 1:31:00 pm

Ok guys here you go, sorry it took so long... memorial weekend, Jason you gave me a file with transparency (AE file) so yours was easily done. I even put it into a fla. and laid a background in to prove the transparency. The white fade is no longer an issue.

Jan yours too can easily be resolved. However send me a project file (AE, FCP) etc... with the actual keyed footage so I can export correctly when I downloaded it it kept coming as a matted black (no transparency on the black). Other wise you wont be able to put in background graphics like I did for Jasons and I assume thats what you want. So link to the correct file and Ill send it back corrected.

I put both of yours in the same folder, test is Jasons and in the root is Jans. If you have any questions let me know.

justinjunda.com/cc.zip



Justin P. Junda


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Jason Metter
Re: FLV w/ alpha channel -- weird white flashes
on May 27, 2009 at 3:34:19 pm

Awesome! Nice work, Justin... much appreciated. Looks like your solution was to render the FLV directly from After Effects, with the alpha premultiplied. Works like a charm.

I am second guessing myself now, because it's working now, but I swear I was not able to render an FLV with an alpha channel directly from After Effects last week. That's why I was rendering a QuickTime with alpha (straight), then converting to an FLV in Media Encoder. So, this solution saves time, as well as delivering a better end product. Love it.

Thank you again, Justin.


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Fred Lacroix
Re: FLV w/ alpha channel -- weird white flashes
on Oct 15, 2009 at 8:13:37 pm

Wow! Just here to thank you all. I've read the whole thread cause I had the same issue... and now that I'm rendering directly via AE, everything looks fine.

thanks again!


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Christopher Hammond
Re: FLV w/ alpha channel -- weird white flashes
on Jan 6, 2010 at 6:02:38 pm

I found this article at the Adobe website that clarifies the Straight vs. Premultiplied discussion and somewhat contradicts the information given here.

http://blogs.adobe.com/toddkopriva/2009/06/flash-flv-alpha-channels-strai.h...


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