Cannot trim clips when “Enable Mercury Transmit” is active — macOS M3 Max

[AI. Lantica]

Hi, I’ve found a consistent issue in the latest Premiere Pro Beta version.

When “Enable Mercury Transmit” is turned on (to preview the timeline on an external monitor), I can’t trim clips normally by dragging their edges in the timeline.

• The clip only shortens or extends a few frames at a time, and then stops.

• I have to release and drag again repeatedly to make any further change.

• As soon as I disable Mercury Transmit, trimming works perfectly again.

This happens with all clips, even those without effects, proxies, or AI enhancements.

Steps to reproduce:

1. Enable Mercury Transmit and choose an external monitor.

2. Try trimming a clip in the timeline.

3. The trim operation becomes laggy or unresponsive.

4. Disable Mercury Transmit → trimming works normally.

System Info:

• macOS 15.2 (24C5022e) — or replace with your exact OS version

• MacBook Pro (M3 Max, 16 cores, 32 GB RAM)

• Premiere Pro Beta (include your build number here)

• External monitor connected via HDMI/Thunderbolt

Expected behavior:

Trimming should work smoothly even when Mercury Transmit is active.

Actual behavior:

Trimming is limited to small frame increments and stops responding until Mercury Transmit is disabled.

Thanks for looking into this — it’s 100% reproducible on my system.

[TheBigRattler99]

Having the same issue, and was about to create a bug report.

Not sure how you figured out it was only when "Mercury Transmit" was enabled, but at least this provides a work-around for now.

Thank You!

System info
    Application: Premiere Pro (Beta) v25.6.0.102
    OS: macOS v15.7.1, RAM: 48.00 GB GB, CPUs (logical): 14

[mivangen]

Hi @AI. Lantica and @TheBigRattler99 - I have reproduced this issue in-house.  Thanks for the report.  I'll update once there is a fix.  Thanks!

[jamieclarke]

Hi @AI. Lantica - Thank you for reporting this issue and providing clear, reproducible steps. The team is aware of the problem and is actively investigating. We’ll share an update as soon as more information becomes available. We appreciate your patience and understanding in the meantime.