I'm trying to render spaceships over a video. In the preview looks great, the ships interacting with the video. But whenever I render, all I get in the video is the spaceships with a white background. Any suggestions?

You need to render in .jpg, .png removes the background.

I applicate your reply-thanks. However, I can't find where to change over to JPG before I render the animation. When I render an images Poser has me select the file type after the render process. Thanks again for your help.

I tried it. AVI video attached to the background and rendered as MP4 video using SuperFly. Worked as expected.

Using single files as output using defaullt PNG: Nothing. Switched Output format to JPEG: Fine!

To change outputformat: If Poser asks for a filename, you will find a drop-down box beneeth the input field. Select JPEG as @Boni suggested.

It worked! Thanks a bunch! I spent way too much time trying to figure that out on my own.

You can also set whatever app you use to composite the rendered frames to ignore alpha. For example in Adobe Premier it's in Interpret Footage when you right click an imported sequence. Then it doesn't matter what format you render to.