At the present time, iScreensaver Designer 5.2 provides support for macOS 10.13 High Sierra, but there are some functional limitations.
Please read the 10.13 High Sierra Tech Note
as well as the Release Notes
Due to changes made by Apple, iScreensaver Designer version 5.2 does not currently support macOS 10.14 Mojave.
Please read our forum post
for the latest updates.
[Solved] Audio hiccup in MOV-based screensaver project
I'm creating a screensaver based on a short, seamlessly looping .mov video file that includes audio. I have it set to loop forever, and on the first cycle the audio plays just fine, but for every subsequent loop it's like half a second is missing from the beginning of the audio part (creating a 'hiccup'), whereas the video loops without any such hiccups.
iScreensaver 22.214.171.1248 on Windows 7 Professional 64-bit