Transparent backgrounds in Quicktime?

Question

Transparent backgrounds in Quicktime?

Looking for some advice on QT encoding...

I have a number of brief QT clips that I would like to use in Keynote presentations. Many of them have uniform white or black backgrounds, and I was wondering if it would be possible to make the backgrounds of these clips "transparent." (I have seen this in commercial Keynote animation packages.)

Is it possible to achieve transparent backgrounds for this purpose using only QT Pro? (I know it's possible with 3rd party software such as After Effects, but I was hoping for something simpler.)

Thanks in advance for any help...

1.67 Powerbook G4 AlBook, Mac OS X (10.4.11)

Posted on Mar 25, 2008 7:13 PM

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Answer 1

Mar 26, 2008 5:35 AM in response to Charlie Perdue

Older (6 and prior) versions of QuickTime Pro had a "color picker" that could set a single color as the "transparency". It's missing in version 7.
Version 7 does allow transparency but it is had to add it into a file that wasn't prepared to be transparent. It requires your file to have an "alpha" channel for the transparency.
Easier would be to use a background that matches the video as it would give the illusion of transparency.

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Answer 2

Mar 26, 2008 6:17 AM in response to QuickTimeKirk

Thanks for the info...

I hate to go with solid black or white backgrounds in Keynote; one of the reasons that I like it is the quality of the graphic backgrounds.

So, even if I try and "add" an alpha channel (say, by exporting the clip using the Animation codec and selecting "millions+") I really don't have any method within QT of selecting which color is to be transparent?

I notice that among the video settings in the QT Movie Properties pane there are options such as "Straight" alpha and "Premultiplied White" alpha... do any of these options help me at all?

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Answer 3

Mar 26, 2008 11:15 AM in response to Charlie Perdue

In my post above "but it is had to add" should have read "but it is hard to add". Darn spelchex.
Exporting using Animation codec wouldn't "degrade" the video quality but it also wouldn't allow you a method of setting the transparency color unless you had some "high end" video editor software.
This is one reason I have two machines and multiple OS's running on them.
Since Apple no longer sells a QuickTime version 6 Pro registration the multiple OS method may not work for you. I routinely work with version 6 and 7 and swap files as needed. Once the transparency level has been "set" even version 7 understands and allows it.
And the color picker method may not be the best use, anyway. It would render any chosen color (from a palette of 32 million) as transparent anywhere it was used in your file. So. A white background around a "talking head" shot would also render the white shirt worn by the "newscaster" as transparent.
Just like an image editor, QuickTime can set alpha "layers" onto a video. But, unlike an image file, video "moves" so it's difficult to add a mask or alpha channel outside a dedicated app like Final Cut Pro or other video editors.
I use "text tracks" in some of my QuickTime files and version 7 shows a "box". Since these text tracks translate as "vector" formats (scale without degrading) I only add them using QuickTime version 6 to add transparency. An example:
http://homepage.mac.com/kkirkster/LemonTrees/LemonTree.qtl

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