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Severe Input Latency & Command Dropping: Playback and Editing Operations (M1 Ultra / macOS Tahoe) #540
Description
System Information
• Hardware: Mac Studio (M1 Ultra, 128 GB RAM, Fully Spec'd)
• OS: macOS Tahoe 26.4.1
• Software: Final Cut Pro (Latest Version) 12.2
• Input Device: Apple Keyboard
• Storage: High-speed Thunderbolt 4 NVMe (External)
• Comparison: DaVinci Resolve (latest) — Running media from the same TB4 drive.
Description
Final Cut Pro exhibits significant performance degradation on flagship Apple Silicon. The issue manifests as extreme latency in keyboard input response—specifically affecting the Spacebar (play/stop), the Delete key (clip removal), and general editing shortcuts.
While DaVinci Resolve remains "snappy" and responsive using the exact same media on the exact same Thunderbolt 4 drive, FCP frequently drops inputs or suffers from "phantom" playhead movement.
The "Time Machine" Trigger
The issue becomes notably worse when Time Machine is performing a background backup. During these periods:
• FCP becomes nearly unusable due to command lag.
• Crucially, DaVinci Resolve remains unaffected. This suggests FCP is failing to prioritize its own I/O or event loop when background system processes (like backupd) are active, whereas Resolve manages these system interrupts gracefully.
Observed Behavior
• Input Lag: Pressing the spacebar or delete key often requires multiple attempts to register.
• Stop Latency: After hitting stop, the playhead continues to drift for several seconds.
• UI Stutter: The interface feels "heavy" and disconnected from the hardware compared to the fluid experience in Resolve.
Steps to Reproduce
1. Connect a Thunderbolt 4 NVMe drive containing working media.
2. Initiate or wait for a Time Machine backup to run in the background.
3. Attempt to edit/playback in Final Cut Pro.
4. Observe the dropped commands and delayed UI response.
5. Perform the same actions in DaVinci Resolve using the same media/drive and observe the lack of any performance hit.
Expected Behavior
As a first-party professional application, Final Cut Pro should offer superior optimization on Apple Silicon. It should maintain a responsive UI and instantaneous transport control regardless of background system I/O, especially on a 128GB M1 Ultra machine.
SCREENSHOTS:
https://adilo.bigcommand.com/watch/8bFBPY1_
Activity
joema4 commentedon Nov 1, 2026
Thanks for the report. I tried the scenario on my M1 Ultra Mac Studio, 128 GB, macOS 27.2, FCP 12.4, Thunderbolt NVME drive for Time Machine backup, and a separate Thunderbolt NVME drive for FCP media and library.
Playback media: multicam composed of two 4k/23.98 10-bit 4:2:2 S-Log3 XAVC-I MXF clips from the Sony FX6. However I did not see the behavior.
For bugs in this category that might not be externally reproducible, yet you can reproduce it on your machine at will, I suggest taking the following data immediately after it happens:
Then just before you reproduce it (assuming it can be quickly demonstrated, say within 15 seconds), do this from terminal and immediately reproduce the problem.
sudo ktrace record ~/Documents/FCP_Issue.ktrace --end-after-duration 15s --compress
Put the result files somewhere they can be accessed.
Purpose:
If you're still interested in this problem, and you capture this info, I'll take a look at it. I don't work for Apple but I have lots of experience in this area. Examples: https://joema.smugmug.com/XCode-Instruments-trace-of-slow-FCP-performance/n-tBwgCJ
alloffroadau-netizen commentedon Nov 1, 2026
have now moved to M5 Ultra and 27.2 so can't really reproduce anymore, will see if it still comes up
latenitefilms commentedon Nov 1, 2026
Given this, I'll close this issue for now. Feel free to re-open if it comes up again.