You upgraded to macOS Tahoe and opened iMovie, only to find it's sluggish. Tasks that used to take seconds now drag on, and simple edits feel unresponsive.

This isn't just you. Since macOS Tahoe launched in September 2025, iMovie users have reported noticeable performance drops. The app works, but not as smoothly as it did on previous macOS versions.

The good news is that you can fix most of these issues without waiting for Apple to release an official update. I'll show you how to speed up iMovie on macOS Tahoe and keep your video editing workflow moving.

What's Actually Wrong With iMovie on Tahoe

iMovie hasn't received a dedicated update for macOS Tahoe yet. The app runs using compatibility mode, which means it's not optimized for Tahoe's new architecture.

The Liquid Glass design that makes Tahoe look stunning also requires more graphics processing. Your Mac is working harder to render the interface, which leaves fewer resources for iMovie's core functions.

Users on Apple Community forums describe the experience as "almost unusable" for basic tasks like deleting clips or applying transitions. The lag isn't consistent either—sometimes iMovie responds instantly, other times you'll wait several seconds for the timeline to update.

Move Your Library to Faster Storage

The biggest performance boost comes from moving your iMovie library to an external SSD. Your internal drive is handling macOS Tahoe's new visual effects, system animations, and background processes. Adding heavy video files to that load creates a bottleneck.

An external SSD gives iMovie dedicated bandwidth. File transfers happen faster, timeline scrubbing feels smoother, and rendering times drop noticeably.

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Set Up External Storage the Right Way

Don't just drag your iMovie library to the new drive. That can corrupt your projects.

Open iMovie and go to File > Open Library > Other. Select your current library, then choose File > Consolidate Library Media. This ensures all your clips, music, and effects are in one place.

Quit iMovie completely. Now you can safely move the library folder to your external SSD. When you reopen iMovie, use File > Open Library > Other again and navigate to the new location.

iMovie will remember this location for future sessions. Just make sure to connect the external drive before launching the app.

Adjust macOS Tahoe's Visual Effects

Tahoe's transparency effects look beautiful but demand constant GPU attention. iMovie needs that GPU power for real-time previews and rendering.

Open System Settings and select Menu Bar. Turn on "Show menu bar background." This eliminates the translucent effect and reduces the processing load.

Next, go to Accessibility > Display. Enable "Reduce Transparency." This setting affects the entire system but frees up significant graphics resources for iMovie.

These changes make Tahoe look slightly less polished, but your video editing experience improves immediately.

Free Up RAM by Closing Background Apps

macOS Tahoe runs more background processes than previous versions. The new Phone app, Live Activities, and Apple Intelligence features all consume memory even when you're not actively using them.

Before starting an iMovie session, quit any apps you don't need. Check Activity Monitor (find it in Applications > Utilities) and look at the Memory tab. If you see apps using hundreds of megabytes, close them.

Don't force-quit system processes unless you know what they do. Focus on third-party apps, web browsers with multiple tabs, and other creative software.

Work With Proxies for 4K Footage

If you're editing 4K video from your iPhone or a camera, iMovie has to process massive amounts of data for every frame. That's especially taxing on Tahoe's current implementation.

Create lower-resolution proxy files for editing. iMovie can generate these automatically: select your clip in the timeline, right-click, and choose "Create Optimized Media." The app will build a smaller version that's easier to work with.

You'll still export your final video at full 4K quality. The proxy files only affect the editing process.

Keep Projects Organized and Small

Large iMovie projects with dozens of clips and multiple timelines strain system resources. Instead of building one massive project, break your work into smaller segments.

Edit individual scenes or chapters as separate projects, then combine them at the end. This approach keeps each iMovie window manageable and reduces the memory footprint.

Delete unused clips from your project rather than leaving them in the timeline. They still consume resources even if they're hidden or muted.

Update to macOS Tahoe 26.2 When Available

Apple is currently testing macOS Tahoe 26.2, which includes performance improvements and bug fixes. The update addresses system-wide issues that affect third-party apps like iMovie.

Go to System Settings > General > Software Update to check for the latest release. Install it when it's available—macOS point updates often include optimizations that app developers can't implement themselves.

Consider Editing in a Different User Account

If iMovie remains sluggish after trying these fixes, create a fresh user account on your Mac. Sometimes accumulated system clutter or corrupted preferences cause performance issues that are hard to track down.

Go to System Settings > Users & Groups and add a new account. Log in there and test iMovie with the same project. If performance improves, the problem lies in your main account's configuration rather than iMovie itself.

The Bigger Picture

iMovie's performance issues on macOS Tahoe aren't permanent. Apple will release an updated version of the app optimized for Tahoe's architecture. That update will likely arrive alongside macOS Tahoe 26.2 or in early 2026.

Until then, these workarounds keep your editing workflow functional. The external SSD in particular makes a dramatic difference—not just for iMovie, but for any creative app that handles large files.

macOS Tahoe introduces powerful features like better Spotlight search, enhanced Apple Intelligence, and improved Continuity options. Once iMovie catches up with an official update, you'll have both the new system capabilities and smooth video editing performance.