OK, I see. I suppose you probably prefer to have black padding on the sides of the image. You would need a Size Position & Rotate filter on each clip to accomplish that.
I suggest you try the Slideshow Generator. It will do that for you and it will make the process faster.
Here are the steps from a high level:
- Save your current project and make a NEW project to use the slideshow generator
- Open all your files in the Playlist. If you choose file->Open and choose many images, they will automatically be added to the playlist.
- In the playlist menu, choose Select->All
- In the playlist menu, choose Add Selected to Slideshow
- Choose the parameters you want and click OK (you probably want to change “Crop” to “Pad Black”