Saving Green screen file with alpha channel

[Renton Maclachlan]

Not sure if the thread title is correct...

Applying Chroma Key and other additional FX to a track uses a lot of computing power. Is it possible to render a track with the Chroma Key etc applied and retain the 'see-through' effect in the rendered file?

I have graphics I need to insert between the CK subject and the background but would like the CK out of the way so the computer doesn't choke on all the FX going on...

I have four tracks which all need to be CK'd...

[David Jimerson]

I believe you can only do it in uncompressed AVI.

Though I haven't tried it for some time and some other new format may be able to do it.

[Gerald Webb]

From Vegas it will be a pain,
Uncompressed 1080p gives you about 1.93GB per 10 sec.
Quicktime PNG may be a better option at around 145MB per 10 sec, but it renders very slow.
Lagarith RGBA is great, but Vegas wont export the alpha channel, it ends up Premultiplied.
If you have After Effects or Premier Pro try Lagarith RGBA, might even be worth downloading a trial just to render out your files, Prob faster than waiting for the PNG's to render, lol.

[Renton Maclachlan]

Thanks guys.

It appears it can't reasonably be done...so I have to devise a workflow that can accomodate the Chroma key without slowing my system down too much.

I have 13 sessions of 15 > 30 minutes which each have four cameras needed to be chroma keyed. I will be switching between cameras but at this point do not know where the switching will occur...and will not know untilI have my graphics in place etc.

I was hoping to do each session in one .veg file, but it seems like this will not work - and that I will need to do each camera in a separate file and bring them together later on somehow...

Just trying out Boris chroma key...seems pretty good...

hmmm...

[Jeff Pulera]

Hi Renton,

You might try the Matrox MPEG-2 I-Frame + Alpha codec (HD version also available).

Can be downloaded here: Matrox Video - Support - Driver Downloads

Under "Products" column, scroll all the way to the bottom to find "Matrox VfW codecs".

Thanks

Jeff Pulera
Safe Harbor Computers

[Seth Bloombaum]

I've been unable to use Lagarith alpha out of vegas too.

QT Animation at "millions +" works fine for cross-platform, but windows QT preview/render performance is too irritating for me to make editing decisions.

I have had to go uncompressed AVI.

Supposedly the Avid DNxHD codecs can support alpha, but they run in the slow QT wrapper, I've not tried to make that work.

I'm very interested to try the matrox codecs, thanks for the link, Jeff.

[Renton Maclachlan]

Hi Jeff

Thanks for that link.

I know nothing about codecs...and am not even sure of the questions to ask regarding them...I've never been this way...

This one you refer to...

How big are the files produced by it?
What is the quality of the files compared with the conventional avi files that come off my SD panasonic GS cameras? This work will evetually be put on DVD and marketed for sale...I want to minimise loss of quality along the production track...
Are these files compatible with Vegas?
Does this condec, once downloaded, go into the render list in Vegas to be selected when desired?
Ummm...any more things I should ask?

[Renton Maclachlan]

I downloaded that codec but can't see how to use it in Vegas...

[Seth Bloombaum]

I've not yet dealt with this codec in particular, but here's how it generally goes:
1) You install a codec using whatever installer the codec maker supplies.
2) Sometimes you have to restart your computer, but the installer might not include this info.
3) You start Vegas and select something to render.
4) Select video for windows, and select the "custom" button. Look through the list of encoders for your new codec.
5) Finding the new codec selection, you then click the "configure" button and try to figure out what the parameters are. If you don't understand them, you leave them alone and hope the default is what you wanted.
6) Render! Review!

If you don't see your new codec in step 4, select Quicktime instead, and then look through that list of encoders.

Usually, free codecs will be wrapped in AVI or QT...

[Renton Maclachlan]

Thanks Seth...tried all that...rebooted...looked in vegas and found it under 'Customise Template'.

I had 'Video for windows (*.avi) > PAL DV Widescreen' selected then in 'Customise Template' chose under 'Video Format', 'Matrox MPEG-2 I-Frame plus alpha'...('Render Alpha Channel' was not selectable...) and rendered....

Unfortunately the transparency was not retained...

...bother.

Anyone have any other ideas...

[Gerald Webb]

Just out of interest,
When you re imported your new clip, did you right click, properties, alpha channel,
Change from None to Straight unmatted?

[Renton Maclachlan]

Gerald. No I didn't...but I've just tried that and it still isn't transparent.

I take it by 'import' you mean 'drop on the time line'...after making the change you suggest...

[Gerald Webb]

Yes Renton, by import, I just meant "bring into Vegas" however it is done.
So it appears your Matrox codec suffers the same as Lagarith, in that, Vegas cant save the alpha channel.
To confirm, you could try saving to the Matrox codec in another NLE and see if the alpha channel works correctly from there.
For instance, I can save lagarith with alpha channel from After Effects but not Vegas.
As slow as it is, Quicktime PNG may be the best option for you.

[Edward Troxel]

I know when you render to uncompressed there's a checkbox you MUST check in order to include the alpha channel information. Is there a checkbox that hasn't been checked?

[Renton Maclachlan]

I won't be able to pursue this for a few days as I'm going away.

If the only way you can render transparency is through uncompressed huge files, then it seems like it is not an option for me...