Premiere Pro crashes when recording voice-over while Blackmagic video playback (Mercury Transmit) is active

Adobe Premiere Pro becomes unresponsive/crashes shortly after stopping a voice-over recording on a timeline that contains video clips, only when Blackmagic video output (Mercury Transmit) is enabled to an external monitor. The issue does not occur when:

• Recording voice-over on an empty/black timeline (no video clips), or
• Blackmagic video playback is disabled while Blackmagic audio monitoring stays enabled, or
• Blackmagic Playback is fully disabled in Premiere's Preferences.

This is reproducible and was isolated through controlled testing across Premiere Pro versions and Blackmagic driver versions.

Environment

• Computer: Mac Studio (Mac14,13)
• OS: macOS 15.1.1 (Build 24B91)
• External I/O device: Blackmagic UltraStudio Monitor 3G (connected via Thunderbolt)
• Blackmagic Desktop Video driver: tested on 12.4.1 and on the latest available version at time of testing — issue persists on both
• Premiere Pro versions tested:
  • 25.0 — works correctly
  • 25.6.2 — works correctly
  • 25.6.3 through 25.6.x — issue occurs
  • 26.0 (release) — issue occurs
  • Downgrade from 26.0 back to 25.6.6 — issue still occurs (ruling out a simple version rollback as a fix, and indicating the cause is not fully removed by reverting the application alone — see Notes)

Steps to Reproduce

1. Open a sequence containing standard HD video clips (no effects, no color correction, short/simple edit).
2. Enable Blackmagic Playback (Mercury Transmit) in Premiere Preferences > Playback, routed to an external monitor via the UltraStudio Monitor 3G.
3. Start a voice-over recording on an audio track under the video clips (Timeline panel > record voice-over).
4. Let the recording run for a period, then stop the recording.
5. Observe: Premiere becomes unresponsive / crashes shortly after the recording stops.

Expected Result

Premiere should stop the recording and return to normal editing without becoming unresponsive.

Actual Result

Premiere hangs/crashes shortly after the voice-over recording ends.

Isolation / Additional Findings

• Does NOT occur when recording voice-over on a blank/black timeline (no video clips present) — i.e., no video needs to be sent to the Blackmagic output.
• Does NOT occur when Blackmagic video playback is turned off while Blackmagic audio monitoring remains active — isolating the issue specifically to the video output path (Mercury Transmit video), not the audio path.
• Does NOT occur with Blackmagic Playback fully disabled in Premiere Preferences (current workaround).
• Lowering playback resolution (down to 1/4) does NOT prevent the crash — ruling out internal Program Monitor decode/render load as the sole cause, since the Blackmagic video output path is not affected by the internal preview resolution setting.
• Pre-rendering the timeline was not conclusively tested as a workaround but is expected to reduce, not eliminate, load on the internal render path (the Blackmagic transmit path is separate).
• macOS diagnostic reports (Microstackshot-based .diag files, generated automatically when Premiere exceeds macOS CPU/disk-I/O thresholds) captured during crashes show:
  • Simultaneous high CPU load from audio mixing (ML::CompilerMixer::GetNextBuffer) and video frame decode/render/prefetch (ML::RenderFrameQueueImpl::ProcessPrefetchRequests, VideoImporterStream) at the time of the incident.
  • Active audio-file writing (BE::AudioFileWriter::WriteToFile) concurrent with this load, consistent with the in-progress voice-over recording.
  • The Blackmagic UltraStudio Monitor 3G is listed as an active Thunberbolt-connected device in the system profile of the crash reports.
  • These are available as supporting evidence and can be shared on request.

Version Regression Detail (important)

The issue does not appear in Premiere Pro 25.6.2, but does appear starting in 25.6.3, and continues through subsequent 25.6.x and 26.x releases. Adobe's public release notes for 25.6.3 do not list any changes related to video playback, transmit, or Blackmagic/third-party I/O — the update was described by Adobe support staff as containing only minor, undocumented bug fixes. This suggests an undocumented change in 25.6.3 may have altered behavior in the video transmit/render path that interacts poorly with the Blackmagic Desktop Video driver under concurrent audio-recording load.

Current Workaround

Disabling "Blackmagic Playback" entirely in Premiere Pro > Preferences > Playback prevents the crash. This is not a practical permanent solution, as it removes external monitor output entirely, including for other project needs.

Suggested Investigation Areas

• Whether Premiere 25.6.3 changed how/when the Mercury Transmit video path is serviced relative to audio capture threads.
• Whether the Blackmagic Desktop Video driver's video transmit thread is blocking or being blocked by Premiere's audio file writer thread specifically during simultaneous record + transmit.
• Reproduction with UltraStudio Monitor 3G and other Blackmagic Decklink/UltraStudio models to determine if this is device-specific or affects the whole Desktop Video driver family.