How Lock Screen video works on macOS Tahoe

On macOS 26 Tahoe and later, the Lock Screen shows the system wallpaper, and macOS plays it rather than the app that installed it. An app gets video there in one of two ways: as a wallpaper extension macOS runs, or as a custom aerial that Apple's own player plays. MacWall's Lock Screen video needs macOS 26 (Tahoe) or later.

What the Lock Screen shows

The Lock Screen is drawn by macOS before you unlock, so no app window can appear on it. It shows the wallpaper chosen in System Settings → Wallpaper. Apple's guide for macOS 26 and 27 says its aerial wallpapers animate as you lock or unlock your Mac, and that by default the aerial you pick also becomes your screen saver. The screen saver is its own choice under Wallpaper → Screen Saver, and the large clock can sit on the Lock Screen alone or on both.

That is why a desktop video on its own never reaches the Lock Screen. A window behind your icons works while you are signed in, but the Lock Screen only plays what macOS holds as the system wallpaper, so the video has to be handed to the system.

Two ways an app hands macOS a video

1. A wallpaper extension. macOS loads the app's extension and gives it the desktop, Lock Screen and screen saver to draw on. One video plays on all three with the same frame, sound included, and keeps playing after the app quits or the Mac restarts. This is MacWall's System Wallpaper mode.
2. A custom aerial. The app converts the video into the format Apple's aerials use, 10-bit HEVC with no audio, and adds it to the system's list of aerials, so Apple's own player shows it on the Lock Screen and as the screen saver. The app can still play something else on the desktop in its own window. This is MacWall's MacWall App mode.

You choose between them in MacWall's Settings → Wallpaper → Playback; new installs on macOS 26 and later start on System Wallpaper. Live Lock Screen and Screen Saver has the steps for each mode, and how to change the Lock Screen on Mac is the full walkthrough.

What you need

• •macOS 26 (Tahoe) or later. Check under Apple menu → About This Mac. Apple's compatibility list for macOS Tahoe 26 still includes some Intel Macs; macOS 27 needs Apple silicon.
• •On macOS 15, MacWall plays the desktop only, and the Lock Screen shows a still from your wallpaper.
• •MacWall Pro or the free 24-hour trial, which includes the Lock Screen.
• •No extra permission. Putting a video on the desktop or Lock Screen needs no Full Disk Access, Accessibility or Screen Recording permission.
• •A moment the first time, with MacWall App only. Converting a 4K video takes several seconds, and the wallpaper's page shows "Preparing the Lock Screen…" with a percentage. Setting the same wallpaper again uses the saved conversion.

Why the Lock Screen goes black after you unlock

Apple's aerial player speeds the video up and slows it down as your Mac locks and unlocks. To do that it reads each frame's HEVC temporal level, a label Apple's Core Media framework attaches to say where a frame sits in the video's hierarchy of frame dependencies. A movie whose frames lack those labels plays on the first lock, fails at unlock, and the next lock is black.

In MacWall's testing, the encoder labelled every frame only when its base layer frame rate was exactly half the video's frame rate. Rounding that value, 12 instead of 11.988 for a 23.976 fps clip, left every frame unlabelled. Current MacWall builds encode at a standard constant frame rate with the base layer at exactly half, check the converted movie, convert again at 30 fps if the labels are missing, report an error rather than install a movie that would go black, and re-check the installed Lock Screen video at launch. With System Wallpaper playback there is no aerial conversion at all.

Fix a black or frozen Lock Screen

1. Update MacWall in Settings → About → Check Now, then open it once. It re-checks the Lock Screen video and converts it again if an earlier build made it.
2. Set the wallpaper again.
3. Quit other live wallpaper apps. Two apps that each keep their own video on the Lock Screen compete for the same system wallpaper choice.
4. Check System Settings → Wallpaper → Screen Saver. If you picked another screen saver after setting a video, macOS shows that one.
5. Switch Settings → Wallpaper → Playback to System Wallpaper, which skips the aerial conversion entirely.
6. Log out and back in, then lock your Mac with Control-Command-Q.

Two things look like faults but aren't. If the screen turns off rather than freezing, that is macOS: System Settings → Lock Screen sets how long the Mac waits on battery and on a power adapter. And a still frame can be a setting: with System Wallpaper, turning off Play the wallpaper while locked, or Pause on battery while the Mac is unplugged, holds the frame on the Lock Screen too.

Still stuck? Troubleshooting covers desktop problems, how macOS wallpapers work covers the layers underneath, and the macOS 27 Lock Screen guide covers the newest release.

Sources

• •Customize the wallpaper on your Mac, Apple Support, accessed 6 November 2026
• •Wallpaper settings on Mac, Apple Support, accessed 5 November 2026
• •Change Screen Saver settings on Mac, Apple Support, accessed 5 November 2026
• •Change Lock Screen settings on Mac, Apple Support, accessed 6 November 2026
• •macOS Tahoe 26 is compatible with these computers, Apple Support, accessed 6 November 2026
• •macOS 27 Golden Gate is compatible with these computers, Apple Support, accessed 5 November 2026
• •kCMSampleAttachmentKey_HEVCTemporalLevelInfo, Apple Developer, accessed 6 November 2026
• •kVTCompressionPropertyKey_BaseLayerFrameRate, Apple Developer, accessed 6 November 2026