The Default black BG is not Black. Its an alpha channel.
So ...make your key and export using a Codec that will allow "transparency" ( eg. millions +)
I dont think you can do it with avi.
FWIW - I use AEFX for this task.
First of all, you should be getting an email every time someone responds. If not, change your settings.
Second, there are a few ways to export video with an alpha channel. One is to use the Quicktime Animation codec. Another is to export to a DPX sequence. There are other still image sequences or video codecs you can use and still maintain the alpha channel.
I don't see aefx
WHEN i EXPORT TO DPX I get dozens of individual unopenable files I just want a single movie with the subject against a transparent background
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You try to make this overly complicated. After your chroma key the transparent parts show up as black since there is no longer any color information and no color means black. You can easily check that by overlaying the keyed clip over another clip, then you see the transparency. Going the way you suggest, keying, exporting with transparency, importing and then exporting again creates generation losses that are not necessary. Just use your keyed clips where you need them in the first place and then only export once.
Harm is correct. It would be better to edit in the program where you keyed out the green. However, if you really must ...
DPX is one file per frame. While you may not be able to open it from Windows, it is only because Windwos has not been told to open them in Photoshop.
The whole point of the DPX file is to have a visually lossless storage of your frames that is designed to be used between applications (just what you want to do): http://en.wikipedia.org/wiki/Digital_Picture_Exchange
However, if you prefer to use another option that you are more comfortable with, you can use PNG.
If you insist on a single video, use the Animation codec for Quicktime.
In any case, you need a picture format or video CODEC that can store an Alpha Channel.
Export the video with the black and use a Luma key in the next application.
Export the video with the black, and then export a video of just the alpha channel as a blabk and white image where black is transparent when used as a track matte, and then in the next application use the video of the alpha channel as a track matte.
Since you haven't said what the other application is or why you want to use it, we are having a little trouble offering a specific solution.
Download the Matrox codec pack here - http://www.matrox.com/video/en/support/windows/vfw_software_codecs/downloads/softwares/ver sion1.0/build33/
Export to .avi using the Matrox MPEG-2 I-Frame HD + Alpha codec (or without "HD" for SD footage).
Safe Harbor Computers
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you need a picture format or video CODEC that can store an Alpha Channel.
The free and lossless UT codec is capable of storing an alpha channel.
Media Encoder has this build in.
Avi: video codec set to NONE, depth set to 32 bit will give transparancy.
The point is that video exported with transparency (32 bit) still shows the transparent parts as black, due to the lack of color information.