A little later: Jarret dropped me a line asking to know what I meant by saying that I figured it out. So here is what I did in case anyone else finds this thread and wants to have a try:
I should point out right at the beginning that this solution gives me a couple of validation errors. But it works perfectly.
First I made a custom page by copying index.php in my theme-directory and adding the lines:
Template Name: Video
At the very beginning, thereby making it a new page template.
At the very end of the same page I added:
function popup(mylink, windowname)
if (! window.focus)return true;
if (typeof(mylink) == 'string')
window.open(href, windowname, 'width=384,height=304,scrollbars=no');
} // -->
I haven't tried this without the html-and body tags. Perhaps that would be more correct. I don't know.
I saved the the template as video.php and uploaded it to my theme directory.
WordPress: Manage/Pages/Create New Page.
Choose "Video" in the Page Template dropdown box instead of Default Template. Create the page.
Under manage pages, the page Video should now be listed. Edit it.
In the Page Content-window, I wrote:
<code><a href="http://www.blabla.com/wp-content/video/video1.htm" onClick="return popup(this, 'video1');if(this.blur)this.blur()" onFocus="if(this.blur)this.blur()"><img src=" http://www.blabla.com/wp-content/video/video1.jpg"/></a></code>
may be completely misused here. I don't know if it's really intended to use when inputing code. It works at least.
This code pops up the html-document "video1.htm" from the thumbnail "video1.jpg"
To my video-directory http://www.blabla.com/wp-content/video/
I have uploaded the video file named video1.mp4 (encoded as streaming quicktime mov-video with an mp4 compression, or else mp4 won't work).
I have also uploaded the thumbnail video1.jpg and the html-document video1.htm, which consists of the following code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<body bgcolor="#000000" leftmargin="0" topmargin="0" marginwidth="0" marginheight="0">
<object classid="clsid:02BF25D5-8C17-4B23-BC80-D3488ABDDC6B" codebase="http://www.apple.com/qtactivex/qtplugin.cab" width="384" height="304">
<param name="autoplay" value="true">
<param name="controller" value="true">
<param name="pluginspage" value="http://www.apple.com/quicktime/download/">
<param name="bgcolor" value="000000">
<embed src="video1.mp4" width="384" height="304" autoplay="true" controller="true" pluginspage="http://www.apple.com/quicktime/download/" bgcolor="000000"></embed>
This should start autoplaying the movie with visible controllers on a black background. You don't really need to specify a background color both in the body bgcolor-tag and the parameter. But I see that this is what I have in my page so I'm sending it on as it is in case some edit I do now without checking breaks anything. If people cannot see the movie, this embed code should offer them a link to where the codec can be found. Don't know if that works in reality. For other video formats, you would need different code with a different object classid and codebase.
There are more QuickTime embed-parameters here if you need them: