Thanks, Rick!  Much appreciated! I was beginning to suspect that was going on but wanted to check here in case I was missing something.  Just to confirm, the website preview clip is SIMULATED to make it look like you are seeing a transparency so that the buyer will know right away that the clip comes with an alpha channel without having to read the fine print.  Actually, when I said it was a website "like Shutterstock", I should've picked a different example as Shutterstock clips don't portray their clips that way from what I can see. You have to read the fine print to see it has an alpha.  Since it's my footage that is being sold, I'm guessing this is something the stock library does at their end, not something I have to mess with.  I'll check with them tomorrow but I'm sure that must be the case.  BTW, what's the opinion here on best codec for broad release of animations to be sold in the broad marketplace?  My animations are primary created in C4d and rendered out in AE.  My live action footage has always been sent to the stock library in ProRes 4444, but I also see a lot of animations being sold with an animation codec.  I'll check with them tomorrow, but was curious about opinions here.  

BTW, sometimes, apparently dependent on the codec maybe, I've seen my clips play back in QT Player with either black or white backgrounds.  Can't figure that one out.  Same clip, just rendered out with a different codec I'm guessing, but I haven't yet had a chance to explore it. Also the clip thumbnail has a black background but plays back with a white BG.  

I did appreciate hearing about the capabilities of QT 7 Pro. While I don't have the Pro version I still use QT 7 which has much more robust features than newer QT players and which was probably why, years back, I didn't purchase Pro.  Sometimes I think Apple really does some stupid things, but that's a whole different topic.

Pete

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If you are playing those movies in a media player on a website you are not seeing through the movies so the background of the website is showing through. What you are seeing is a representation of the transparency grid that you see in an app like Photoshop, Illustrator or After Effects. They create that grid as a graphic and put it at the bottom of the layer stack and render a file for the web. Then the product is delivered in a format that supports transparency.

If you could download open one of the sample clips from a site like Shutterstock and you put that clip in an AE project or checked for an alpha channel you would see that there is no transparency in the video. 

If you purchased one of those clips with a transparent background and loaded it in any media player the transparent part of the clip would be black because there is nothing there to see. You would not see your desktop through the media player. That’s not how media players work.

I do not recall ever seeing a desktop behind Quicktime Pro either. No video = no pixels = black background.

I hope this helps.