ci(verify): real-capture recording oracle on GitHub-hosted Windows

[richiemcilroy]

Runs the real-capture recording oracle (crates/verify/tests/recording.rs) on Windows. It records a marker stimulus through Cap's real Studio and Instant pipelines, with Windows Graphics Capture and Media Foundation, and checks every frame and audio marker against the host-clock truth, as it already does on macOS.

Where it runs

Verify recording gains a real-capture (windows-2022) job on GitHub-hosted Windows, and the required Verify recording gate now requires it too.

• Runner choice. Blacksmith Windows VMs run jobs in session 0, which has no desktop to capture (CopyFromScreen: "The handle is invalid", probe runs 38997642473 and 38997747111). Hosted runners run jobs in the interactive console session, where Windows Graphics Capture works.
• No audio endpoints. Hosted Windows has none: the stimulus stays silent, Cap records without system audio, and recording/instant/system-only is allowed to report unsupported. The microphone and camera are the harness's synthetic feeds, as on macOS.
• Build time. The job builds with the ci-verify profile through engine-verify-setup: about 4 minutes with a warm cache.

Harness changes

Piece	macOS	Windows
Host clock	mach ticks	QueryPerformanceCounter, the clock Cap stamps Windows capture with
Input thread scheduling (cap_verify::sched)	time-constraint policy	THREAD_PRIORITY_TIME_CRITICAL, 1 ms timer resolution, high-resolution waitable timer waits
Stimulus presentation	softbuffer	layered window updated with UpdateLayeredWindow
Synthetic camera frames	CVPixelBuffer sample buffers	NV12 in a Media Foundation memory buffer, as the Windows camera feed hands them over
Crash snapshot	APFS clone (cp -cR)	file-by-file copy

• Stimulus tearing. softbuffer presents on Windows with a GDI blit that the compositor captured half done: markers with the new picture's top rows and the old picture's bottom rows (3 to 19 unreadable frames per recording). A flip-model DXGI swap chain was rejected by the hosted Hyper-V display. A layered window hands the compositor whole pictures: 0 unreadable frames since.
• Synthetic microphone (crates/recording/src/feeds/microphone.rs, test-utils only). It now registers its stream health, which a recording subscription on Windows and Linux attaches to and a real input registers when it opens.

First results, fast tier (run 39005636945)

Case	Windows
recording/studio-screen/fragmented	pass
recording/studio-screen/gated	pass
recording/instant/screen-mic-system	pass
recording/instant/gated	pass
recording/studio-recovery/crash	pass
recording/instant/late-mic	xfail: the existing late-microphone mechanism, now listed for Windows too
recording/studio-camera/startup-drops	xfail: Windows camera frame pacing (below)
recording/instant/system-only	unsupported: no audio device

What it found

• Windows camera frame pacing (in cap-v0.6.0 too). When no camera frame arrives within one frame interval, the Windows camera encoders re-encode the last frame stamped one interval later. That is the slot a slightly late real frame is stamped for, so the real frame lands on the same timestamp and the muxer moves it by one tick. Recordings had 11 to 41 duplicated camera frames, and camera-mic sync of -18 to -38 ms. The fix is a separate pull request, proven against this job.
• Camera start offset on Windows. For the first 3.5 s, camera frames sit 66.7 ms off their steady offset. Under investigation.

Confidence Score: 5/5

The PR appears safe to merge, with no new blocking issues found.

Summary

Adds real recording checks on GitHub-hosted Windows and requires them in the recording gate.

• Recording checks now run on Windows and macOS.
• Windows recording checks now compare captured markers with Windows-clock times.
• Crash recovery now preserves live recording snapshots on Windows.

No new actionable issues were found in the changes since the previous review.

_{Reviews (2) · Last reviewed commit: "fix(verify): Windows stimulus audio uses..." · Reviewed by Greptile}

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
cap-status	Ready	Preview	Oct 17, 2026 11:02pm UTC

[capy-ai]

Capy found 1 potential issue (1 medium).

View 2 other findings in Capy.

[richiemcilroy]

@greptileai review

[capy-ai]

Capy found no issues.

[capy-ai]

Capy found no issues.