Fix After Effects Preview Engine Failed on macOS Sonoma

After Effects on Mac Sonoma shows 'Preview engine failed to initialize' when using GPU-accelerated previews. Fix by resetting GPU preferences and clearing cache.

You're working in After Effects on a Mac running macOS Sonoma 14.x. Everything's fine until you hit the spacebar to preview your composition. Instead of the RAM preview playing, you get a dialog: Preview engine failed to initialize with the code PREVIEW_ENGINE_FAILED. This usually happens right after a macOS update, a driver change, or when you've switched between internal and external GPUs. It also shows up if you've been switching between Mercury GPU Acceleration and Software Only rendering mid-session.

The root cause is pretty simple: After Effects can't initialize its GPU-accelerated preview engine. On Sonoma, Apple's Metal graphics stack changed how apps talk to the GPU. After Effects stores its GPU settings in a preferences file, and that file can get corrupted or contain a reference to a GPU that's no longer available. When that happens, the preview engine fails to start, and you're stuck staring at a frozen composition.

The Fix: Reset GPU Preferences and Clear Cache

Skip the usual 'restart your Mac' advice—you've probably already tried that. The real fix is to delete the GPU preferences and clear the disk cache. Here's how, step by step.

Quit After Effects completely. Press Cmd+Q, or go to the After Effects menu and choose Quit. Make sure it's not running in the background—check the Dock for a dot under the icon.
Open Finder. In the menu bar, click Go > Go to Folder. Or just press Shift+Cmd+G.
Type the preferences folder path and press Return:
```
~/Library/Preferences/Adobe/After Effects/
```
You'll see a folder with a version number, like 24.0 or 23.6. Open that folder.
Find the file named After Effects Preferences.txt—it might have additional numbers in the name, like After Effects Preferences 17.0.txt. Select it and move it to the Trash. Don't worry, this file is recreated the next time you launch After Effects. You'll lose your custom keyboard shortcuts and UI preferences, but not your actual projects.
Next, clear the disk cache. Go back to Finder and press Shift+Cmd+G again. Type:

~/Library/Preferences/Adobe/After Effects/

Wait, that's the same folder. Hold on—I meant the cache folder. Let me correct that.

Actually, the disk cache lives in a different place. Press Shift+Cmd+G and enter:

~/Library/Caches/Adobe/After Effects/

You'll see subfolders for each version. Open the one that matches your After Effects version (e.g., 24.0). Inside, delete everything you see. These are temporary files that were used for previews—clearing them forces After Effects to rebuild the cache from scratch. This alone often fixes the preview engine error.

Restart your Mac. I know I said skip the restart, but that was before we cleared the cache. A fresh start ensures that the GPU driver is reinitialized cleanly.
Launch After Effects. It will create a fresh preferences file. Go to After Effects > Preferences > Display. Under Renderer, you should see Mercury GPU Acceleration selected. If it's set to Software Only, change it to Mercury GPU Acceleration and choose your GPU from the dropdown if available.
Try a preview now. Press the spacebar. You should see the preview engine initialize without errors. If it still doesn't work, move on to the next section.

Still Seeing the Error? Check These

If the error persists, the problem might be deeper than a preference file. Here are three things to check in order.

1. Verify After Effects is up to date

Adobe pushed specific fixes for Sonoma in After Effects 24.2 and later. Open the Creative Cloud app, go to Apps, and click Update next to After Effects if it's available. Running an older version on Sonoma is asking for trouble.

2. Check your GPU's Metal support

Sonoma requires a GPU that supports Metal 3. That's most Macs from 2016 onward, but older Mac Pros or Macs with AMD Radeon 200 series cards might not cut it. To check, go to Apple menu > About This Mac > System Report > Graphics/Displays. Look for the Metal line. It should say Metal Support: Metal 3. If it says Metal 2 or lower, you won't get GPU acceleration working—switch to Software Only in After Effects and live with slower previews.

3. Use the After Effects Clean Boot

Sometimes third-party plugins or startup items interfere with GPU initialization. Restart your Mac, hold the Shift key until you see the login window, and release it. That boots into Safe Mode. Open After Effects, try a preview. If it works, the issue is a conflicting plugin. Remove recently added plugins from /Library/Application Support/Adobe/Common/Plug-ins/7.0/MediaCore/ one by one until the error stops.

One more thing: if you're using an external monitor via a USB-C dock, try plugging it directly into the Mac. Some docks don't play well with Metal's GPU handoff, and that can trigger this exact error.

That's the whole fix. It's not glamorous, but deleting that preferences file and clearing the cache resolves nine out of ten cases. If you're still stuck after all this, the last resort is a full uninstall and reinstall of After Effects—back up your presets and scripts first. Good luck.