This has been submitted as FB8745172

Also seen in the very popular Aerial screen saver https://github.com/JohnCoates/Aerial/issues/1107

More info This only seems to affect Mojave (10.14) The bug seems to crop up depending on the order in which you installed Safari 14 and Security Update 2020-005. If you installed Safari 14 after the security update, then everything is fine. see mrmacintosh.com/mojave-2020-005-security-update-causing-major-problems-updated/

I've seen this on macOS and it seems to be caused by some videos being rendered in hardware. A solution is to use javascript to create a canvas, draw the currebt video frame into the canvas, then show the canvas while you take the screenshot. That seems to force the video content to really get included in the webView properly and then it shows up in the screenshot.

Interesting - if seems that if we set a 0.5 second timer to call StartAnimation from within the Initialize method, it works again. This is probably safe as long as your screensaver can gracefully deal with StartAnimation getting called more than once.

If I can come up with a reproducible case, I will submit a FB report. I think I'm now seeing the problem with Apple screensavers as well. If anyone can try this test, I'd appreciate it: Test 1: Open System Prefernces / Desktop & Screen Saver Select the "Message" screensaver Click Screen Saver Options and enter some text to display "foobar" Result: the apple logo and text are displayed. Test 2: Close System Prefernces Open System Prefernces / Desktop & Screen Saver Result: although the Message screensaver is selected, the Preview is now blank If you click Screen Saver Options and then Cancel, the Preview now shows up Repeating the test with the "Hello" screensaver does not show the bug.

Here's what I see when it's not working, and I can reproduce this issue on 3 different 12.1 systems (M1 and Intel):

Submitted as FB9835060

This bug is still present in 12.2 release version (Silicon and Intel).

I am no longer seeing this issue in the first beta of macOS 13 Ventura (22a5266r)

Still happening in Beta 3 - I've narrowed it down a bit, it appears that any use of WkWebView in a x64 Intel app no longer functions on M1 / ARM macs: Instead, the WebKit process crashes. A standalone ARM build, or a Universal Intel/Arm build work fine. Apple: this is a very bad regression, any insight? I have updated FB11786440 with an XCode sample project to illustrate the crash.

Thanks @eskimo the FB cases we know about are FB12023530 and FB12007471 - the thread which has the most technical details is this one: https://github.com/JohnCoates/Aerial/issues/1286 Note that the bug appears to be random and intermittent, so one successful test doesn't mean it's not happening. Test multiple times.

Unfortunately this bug has been improved, but not fixed. In 13.4 RC, a system with 2 monitors works about 95% of the time. On a system with 3+ screens, the failure rate is 100%. Submitted a new FB case FB12179420 Discussion continues here: https://github.com/JohnCoates/Aerial/issues/1286

@eskimo We are also getting reports of failures in first-party Apple screensavers using 13.4 on multi-monitor systems - in particular the Shifting Tiles screensaver has random blank screens when starting on 2 or 3 monitor systems. Shifting Tiles: when using the "Options / Source: Colors" (which doesn't use photos, just blocks of color) it seems to work fine on 2 or 3 monitor systems. However, if I choose "Options / Choose Folder" or "Options / Photos Library" then I can see some sort of malfunction: With 2 monitors: after the screensaver starts, I get 2 blank screens for about 20 seconds. After 20+ seconds, then both screens start working. With 3 monitors: after the screensaver starts, I get 5 seconds of blank screen, then monitor 1 starts, then another 5 seconds, monitor 2 starts, then another 5 seconds and monitor 3 starts. With repeated testing, the pattern is somewhat random: sometimes 1 and 2 start right away, followed by 3 about 5 seconds later.

I'm digging into this in more depth, don't have specific answers to all the issue yet, but am discovering some workarounds, and will post back when I have things sorted out. Feel free to contact me directly if you want info sooner - I'm active in a few places, including https://github.com/JohnCoates/Aerial/issues