how to export an openGL scene with alpha channel?

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mat_kinotek

hello list !!
i have a problem: I have a openGL patch wich render a bunch of
particles; I am exporting this openGL
scene in "animation" .mov format, and what i want to do is to export
the background with the alpha channel.
I know the "animation" compression can have the alpha channel, but
from the openGL renderer i have no clue
of how to set the alpha value of the background to 100%. The
erase_color have the argb, but when i put rgb
values to 0 end the alpha value to 1 the background is black and the
exported .mov file doesnt seems to have
any alpha channel.
any hint??

ps.
to render and export my patch I m using the (fantastic!!) render node
by Randy Jones - http://2uptech.com/
but the process would be the same also without it..

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Mattia Casalegno
http://www.kinotek.org
mat@kinotek.org
++393332152448
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