To add a watermark to your uploaded videos, you have to use our transcoding service, Encode Magic. From the "Integrations" section (1) on the "System settings" page, go to the EncodeMagic (2) tab, and check the "Enable Watermark" (3) option.
Click on "Save" to confirm. If your EncodeMagic integration is active and properly configured, all your uploaded videos are now set to be with watermarked with your "System logo" (4) (as uploaded in the "Home > System Settings > Appearance" page).
Note: To make sure your EncodeMagic integration is enabled correctly, see this article.