Go to Library and upload images or videos. You can sort them into folders.
Why videos are converted
Many signage boxes are low-cost devices with little memory. VisionMagic makes a light copy of every video (720p, a widely supported format, and a turned copy for portrait screens) and sends that copy to the screens. Your original file is kept, and you can download it again at any time.
A video can play on screens once its copy is ready. This usually takes a short while after upload, depending on its length.
Replace a file everywhere
Use Replace file on a file to swap in a new version. Every playlist and screen that uses it switches to the new version once it is ready.
Where a file is used
Open a file to see which screens should have it, whether each screen has downloaded it, and which playlists use it. From there you can also take it off screens or out of playlists.