I’m seeing a device/OS-specific AVFoundation issue on iPhone 14 Pro running iOS 26.6.
A secondary AVCaptureVideoDataOutput is used to provide an unstabilized monitoring feed while the main recording connection is stabilized. During continuous zoom changes, frames from the secondary output continue arriving and scene motion remains live, but its visible zoom/crop/FOV intermittently remains unchanged and then catches up. The saved recording remains smooth and reflects the requested zoom correctly.
Minimal configuration:
- Device: iPhone 14 Pro
- iOS: 26.6
- Physical Ultra Wide camera
- 1920×1080 at 30 fps
- SDR, 8-bit YUV
- Main VDO: 420v
- Main connection stabilization: .cinematicExtendedEnhanced
- Auxiliary VDO: 420f
- Auxiliary connection stabilization: explicitly .off
- automaticallyConfiguresOutputBufferDimensions = false
- deliversPreviewSizedOutputBuffers = true
- alwaysDiscardsLateVideoFrames = true
- Deferred start disabled
- Both outputs use a serial delegate queue
The auxiliary output is displayed directly without image processing.
During continuous videoZoomFactor updates:
- AVCaptureDevice.videoZoomFactor advances correctly.
- The UI zoom value advances correctly.
- The main recorded output zooms smoothly.
- Frames from the auxiliary output continue arriving and scene motion remains live.
- Only the auxiliary output's visible zoom/crop/FOV intermittently holds at an older value and then catches up.
- This is not a complete preview-frame stall: camera movement remains visible during the periods when zoom does not visually advance.
- The problem occurs with any non-Off stabilization tier in the production app because that configuration installs the unstabilized auxiliary output.
- Stabilization Off removes the auxiliary topology, and zoom then appears smooth on the main preview feed.
A standalone capture sample reproduces the problem without the application’s writer or rendering pipeline.
Current device matrix:
- iPhone 14 Pro, iOS 26.6: reproduces.
- iPhone 13 Pro, iOS 18.6.x, same released application version: does not reproduce.
- iPhone 17 Pro, iOS 26.6, isolated sample: does not reproduce.
- iPhone 14 Pro, iOS 27 beta 5: testing in progress — result to be added.
The issue was initially reported with HEVC/Apple Log capture, but it remains reproducible after reducing the graph to 1080p30 SDR8.
Questions:
- Is using two video-data-output connections with different stabilization modes—Extreme on the recording output and Off on the monitoring output—a supported configuration?
- Is delayed propagation of zoom geometry/crop to a secondary video-data output known on iPhone 14 Pro/iOS 26 when another output connection is stabilized?
- Is there a recommended AVFoundation topology for obtaining a low-latency, unstabilized monitoring feed while separately recording stabilized video?
- Are there output or connection properties that must be set to make videoZoomFactor geometry changes propagate synchronously to both outputs?
I can provide the standalone sample project, screen recordings, connection-mode logs, buffer PTS/arrival cadence, and a sysdiagnose.
EDIT: Issue seen on iOS 27 beta 5 devices as well. No such issue is seen in iOS 18 devices.