Saving movies containing an alpha-channel

[blissomatic]

Hello folks!
I know it is possible to save a png with a transparent background but is this also possible to do as a movie? My goal is to get it in to after effects and make into 3d-layers and make the trees for instance cast shadow. Always when i open a movie in after effects the background is either white or black if you made it transparent before rendering.

Would really appreciate some help here!

/ henrik

Oh and keying out the white or black is not an option as it works poorly. Choosing add or multiply as blending modes are neither as i want the lights to cast shadow from the tree object and not from the square image file.

[MtnViewJohn]

Very strange. The movies should be 32-bit with alpha channel. But they clearly are not. I will look into it.

[MtnViewJohn]

But while we work on this you can use the command-line version of Context Free to create the movie as a series of PNG files. Alpha works fine in PNG output. You just need a program that takes a set of PNG files and turns them into a movie.

[MtnViewJohn]

I have an edit that may fix the problem but I have no way to test it. Do you use the Windows or Mac version of Context Free?

[MtnViewJohn]

Can you download this movie file: http://www.contextfreeart.org/download/ ... ha_hsg.mov and tell me if it has an alpha channel that After Effects can use?

It looks totally black in QuickTime Player. But that is just because the transparent parts are drawn as black and the opaque parts happen to be black too. In Quartz Composer there appears to be a correct alpha channel.

[blissomatic]

hey john!
great that you're working on it! sorry to say though, it looks totally black in after effects. the file reads as millions colors+ (premultiplied)
should it maybe be straight instead of premultiplied?
i don't know.

thanks for a great application anyway!

[MtnViewJohn]

Yes, it is a black image on a transparent background with premultiplied alpha, so it would look totally black by itself. You weren't able to composite the movie track with an image or add another movie track behind the one with alpha? In Quartz Composer I can definitely see an alpha channel.

Here is another movie that has some color along with a transparent background:
http://www.contextfreeart.org/download/ ... alpha2.mov

[blissomatic]

Hey John!

That movie worked for me when I changed the alpha from premultiplied to straight in after effects!
So was that just a regular render from context free? Just transparent background then render?

Great then!