Alpha Channel?

OhMyGosh wrote on 10/14/2009, 11:34 AM

I imported a composition from After Effects as .avi. It has a 'shattering' effect in which I want the underlying video to show through as the top layer shatters. All I can see is black until the clip is through, at which time the bottom clip shows. What am I missing this time........? Is it some sort of Alpha issue?
By the way, my 7 second composition is over 1G in .avi :O If I were to render to mpg2, would VMS rerender and loose quality, or would it 'smart render?' Thanks. Cin

Comments

Terry Esslinger wrote on 10/14/2009, 12:22 PM

Right click on the media on the time line. Choose media, properties and check the box to turn on the alpha channel. I don't know why Vegas insists on having the alspha turned off as the default.

OhMyGosh wrote on 10/14/2009, 1:12 PM

Thank you Terry. I thought that was going to be a God send, and maybe with a little tweeking it will be. I did as you said, but there was no 'box' to 'check'. I did find the alpha drop down list with five choices and tried each one with no luck, but I feel you are on the right path, I think there must be one added step along the way that is missing. Thank you again. Cin

Terry Esslinger wrote on 10/14/2009, 8:23 PM

I,m not sure that avi will support alpha channel. Are you sure you rendered it out of AE with alpha channel?

Rory Cooper wrote on 10/15/2009, 12:23 AM

OMG ….AVI uncompressed will support Alpha channel

Most AVI codecs do not support Alpha, some do. so when rendering for Alpha , render uncompressed AVI
Then select alpha straight as Terry said

Rory Cooper wrote on 10/15/2009, 12:31 AM

If you have a clip with a solid black embedded alpha and some shatter stuff going on

Then double up the clip
On the top clip convert to a solid black and white…use mask gen fx and also add light and dark fx to get the white solid then multiply the mask
And place your other media on the bottom

OhMyGosh wrote on 10/15/2009, 7:35 AM

You were absolutely right Terry. Here is the answer straight from Mt. Olympus (actually Adolfo Rozenfeld, who is an Adobe employee and After Effects guru):
'To embed an alpha channel in a video file, you have to set the Channels menu in the Render Queue's Output Module to "RGB+Alpha".

Now, the tricky part is that for most of the standard AVI codecs you only get "RGB" or "Alpha" as options. This is because they are 24 bit codecs, ie they lack the extra 8 bits needed to store transparency (don't mistake this "bit talk" with color depth, which is about bits per channel).. Choosing "No compression" in the Video for Windows (AVI) format options will definitely let you set the channels to RGB+Alpha. But it will also produce a very, very large file. Unfortunately, you'll see the selection of standard AVI codecs with alpha support is rather limited, and that's why so many users choose the Quicktime format with Animation or PNG codecs - same uncompressed quality, with somewhat reduced file sizes and alpha support.'
Having done that, it still didn't work until I changed the alpha setting as you said Terry. Also, thank you xfx for your help and input. That is a nice work around :) Cin