What type of node do I need to ...

Put together 3 videos (AVI Raw), each of them with their respective particles rendered with alpha?
I know I’ll need an AlphaOver to composite the particles over the other video, but what I don’t know is what other node I need to connect the other 2 videos I have (the continuation of the movie).

Thanks in advance guys :slight_smile:


I’m not sure what you mean but for starters you need two input nodes to load the two videos (live and cg), an alpha over node to overlay one on top of the other and a composite node to render out. That’s it. Repeat for the other two live videos overlaying the cg elements following the above setup. Then switch to the VSE and assemble all three rendered videos in one.

Oh, I see! So the actual assembling is not done with nodes. Thank you so much blendercomp :slight_smile:
Actually, couldn’t all be done in the VSE then?


It works just fine when I use PNGs for testing the alphaOver nodes. But it doesn’t when I use the AVIs :frowning:
I noticed that the PNG thumbnail shows a “white background”. And the AVI thumbnail shows a “black background”. Could it be that my AVIs are not rendering with their respective alphas? How could I inspect the video file to know if it has an alpha? And moreover, how to render its alpha?
I have been selecting the “RGBA” button in the Render/Output settings. It worked for the PNGs
Any info on this would be greatly appreciated guys.

Btw, I’m using Blender 2.5…


Well, actually it can all be done in the compositor if you want it too.
As for the VSE, in principle it’s also perfectly doable there using an alpha over blend mode but you’ve got much more control in the compositor.

Keep in mind that avi does not store alpha channel data so the idea is to use image sequences in a format such as png that does store transparency data.
To see if a video source has alpha feed the alpha output socket of the input node to a viewer node. Transparent areas should appear as white, non-transparent as black.

Bear in mind that not all file formats have Alpha information …

Thanks a bunch for the info guys.
I’m using a sequence of PNGs as suggested.

blendercomp, would you say the Compositor offers more control than the Nodes Editor for this task?


What’s wrong with this noodle?! :frowning:
It’s only rendering the background.
Oh, I know! I still need to change the AlphaOver/Premul to 0.5. Now it’s working! :slight_smile:


The compositor IS the node editor!
And yes, regardless of names, it offers absolute control.

It’s really late around here and I’m really really sleepy so maybe it’s just me but there’s absolutely nothing wrong with the output! :slight_smile:
What is wrong is that you seem to combine two image inputs, one of which apparently has no data -or is fully transperent at frame 1. So it makes no sense to overlay them at all! :0
You’re overlaying a fully transparent image over another image so nothing is gonna show up.
What are you really trying to accomplish? %)

I guess I spoke too soon :frowning:
Testing the background and the alpha at frame 250 worked fine. But doing the animation (all the 500 frames sequence) is not the same. It only renders the 1st frame over and over.
Please see above noodle update.
What could be wrong?


I may have got it now. I had Premul selected in the rendering settings, Shading/Alpha/Premul, I changed it to Sky now.

Ok, it worked now. Here’s the updated noodle, settings used and a little explanation for some closure:


Each of the Image nodes above load a sequence of PNGs. The one below is particularly important as it has alpha data (reason why PNG was chosen).
I don’t know if it was a coincidence but as soon as I started outputting to MPEG as oppose to AVI I stopped getting corrupted files.