HLG External Monitoring Bug in Final Cut Pro 11.1.1 on macOS 15 (Sequoia)

Dear Apple Team & Community,

I would like to share a reproducible issue that affects Rec. 2100 HLG projects in Final Cut Pro (FCP) 11.1.1 on macOS 15 Sequoia when an external HDR display is used as the primary viewer. I hope the detailed information below will help engineering isolate the root cause and provide a timely fix, as it currently limits professional HDR workflows—especially for HLG deliverables.

1. System Configuration

ComponentDetailsHardware16-inch MacBook Pro (M4 Max, 38-core GPU, 64 GB RAM)macOS15.0 (Sequoia)Final Cut Pro11.1.1 (Build — latest public release)

All automatic brightness, True Tone, and Night Shift options are disabled. The external display runs at its native resolution and refresh rate.

2. Steps to Reproduce

1. Create a new Library → set Color Processing to Wide Gamut HDR.
2. Create Project A

• • Video Properties: Rec. 2020 PQ, 25 fps
  • Add a 100 % white generator for 10 s.

1. Create Project B

• • Video Properties: Rec. 2020 HLG, 25 fps
  • Add the same white generator for 10 s.

1. In Preferences ▸ Playback

• • Audio/Video Output: external display (A/V Output enabled)
  • Display HDR as Tone-Mapped unchecked.

1. Toggle between Project A and Project B while monitoring waveform and perceived brightness on the external display.

3. Expected vs. Actual Results

ConditionExpectedActualProject A (PQ)Waveform flat at 1 000 nits; visual white close to monitor’s peak luminance.✔ As expected.Project B (HLG)Waveform at reference 75 % HLG (~1 000 nits); visual white identical to PQ project.✖ Waveform is clipped to ~100 nits; image appears ~4–5 × darker than PQ.

Switching HLG material into a PQ timeline instantly restores correct brightness, confirming the anomaly is HLG-specific rather than hardware-related.

4. Troubleshooting Already Performed

• Re-cabled with certified HDMI 2.1 and another DisplayPort 1.4 cable — no change.
• Forced monitor to fixed HDR presets (DCI-P3 & Rec. 2020) — no change.
• Reset FCP preferences and rebuilt ColorSync profile caches — no change.
• Created identical test projects in FCP 10.7.4 on macOS 14.6 (same machine via external disk) — HLG output is correct, suggesting a regression introduced in macOS 15/FCP 11.x.
• Verified identical behaviour on a second HDR display (LG 32EP950) — issue persists.

5. Analysis & Hypothesis

Preliminary testing indicates that the ColorSync pipeline erroneously applies SDR tone-mapping to HLG frames en route to the external HDR viewer when the GUI runs in macOS 15. PQ footage bypasses this path correctly, so the root cause is likely an HLG-handling regression in either:

• CoreDisplay / ColorSync HDR path on macOS 15, or
• The new “Extended Dynamic Range” (EDR) compositor FCP 11.1.1 leverages for HLG.

Because Dolby Vision mastering is PQ-centric, many editors may not notice; however, broadcasters and live-HDR operators who rely on HLG cannot currently trust on-set or editorial monitoring.

6. Impact on Workflow

• Creative accuracy — Impossible to color-grade or QC HLG deliverables in real time.
• Time & storage — Requires converting existing HLG libraries to PQ, duplicating media and forcing an HLG→PQ LUT, which is not ideal for broadcast deliverables.
• Confidence — Client monitors driven via A/V Output misrepresent luminance, risking rejection or costly re-grades.

7. Request

Could the engineering team please:

1. Confirm whether HLG monitoring is expected to work in FCP 11.1.1 on macOS 15 when “Display HDR as Tone-Mapped” is disabled.
2. Investigate ColorSync tone-mapping behaviour for HLG on external HDR devices.
3. Advise if a short-term workaround exists (e.g., beta patches, hidden flags, or specific display profiles).
4. Document any known limitations in official support articles or release notes.

8. Diagnostics Available

Please let me know the preferred channel for transferring these assets.

Thank you for your time and for the ongoing improvements to Final Cut Pro. I am happy to run additional tests or provide further data to help resolve this regression.

Best regards,

DoP / HDR Finishing Editor

Los Angeles, CA