alpha channel

[matt_knelsen]

Hi everyone,

We are working in a project in which we need to set up two layers, and the upper layer needs to be encoded with alpha channel, so we can work with "background" and "foreground" videos. I'm using SUPER converter to encode the videos from .mov to .avi mpg2. I've rendered the movie in After Effects in .mov, with the alpha channel embedded. Does anyone knows how can I setup SUPER or other encoding tool to include the alpha channel? One detail: the final .avi file must contain the audio stream as well.

Thanks!

[Daniel Kaminski]

Hi Matt,

There is no AVI codec right now that will support what you are trying to and have acceptable quality and playback performance. The best codec for playing back embedded alpha channel is Quicktime Animation. The problem with quicktime Animation is that it is nearly uncompressed and so you might run into playback performance problems. (It might work with 1 or 2 SD Videos but HD will be a problem, it also depends on the videocontent).

Another way of doing this is using 2 mpeg2 videofiles. Just render out your Movie and your alpha channel seperatly from After FX, so that you have one regular mpeg2 Video and one regular mpeg2 video with alpha information (it is a black and white video).

After that take a look at the following tutorial that explains how to use alphablend modes.
viewtopic.php?f=2&t=334&p=655&hilit=alpha#p655

One last note regarding audio. In order for pandoras box to sync videos together the audio must be played back seperately, best will be a seperate pcm wav file.

I hope that works for you.

Daniel Kaminski