perf(recording): finalize and validate audio alongside the video remux

[richiemcilroy]

After Stop, finalization remuxes the fragmented recording into progressive files and validates every track. Each audio track was fully decoded twice: the input fragments before the remux, then the output file after it. Both decodes ran one after another and after the video concat, so on macOS the Instant share link waited for all of it (finalize_with_publication → finalize_staged). The GPUI app and the CLI both go through this path.

gantt
  dateFormat X
  axisFormat %L ms
  section main (Instant 600 s)
  input audio validation :a1, 0, 470
  video concat + validation :a2, after a1, 530
  audio concat + merge :a3, after a2, 230
  output audio validation :a4, after a3, 520
  section this PR
  video concat + validation :b1, 0, 530
  audio validation + concat :b2, 0, 520
  merge :b3, after b1, 190
  output audio + merged video validation :b4, after b3, 520

Loading

• Instant (crates/recording/src/recovery.rs): input audio validation and the audio concat run on a scoped thread while the video concat runs. The final audio check runs alongside the merged-video check. Its result is reused only when that check didn't rewrite the file.
• Studio: per segment, audio finalize and its output validation run alongside the display/camera concat (finalize_segment_video / finalize_segment_audio). The mic and system-audio input validations run in parallel (validate_recovered_audio_in_order).
• Every check still runs on the same files. When more than one track fails, the error returned is the first in the original track order. If a thread can't be spawned, the work runs serially as before. The new threads get 16 MiB stacks.
• Every finalized file in the bundle is byte-identical to main, apart from publication-receipt.json, which hashes mtimes and inodes and differs between two main runs too.

Benchmark

Finalize wall time (M4 Max, interleaved A/B, median [range]):

Fixture	main	This PR	Change
Studio 60 s (mic + system audio + camera)	477 [434-499] ms	392 [384-428] ms	−18%
Studio 180 s	1571 [1426-1863] ms	1371 [1263-1719] ms	−13%
Instant 600 s	2158 [1909-2443] ms	1481 [1341-1621] ms	−31%

	main	This PR
Instructions (Studio 180 s)	24.205e9	24.197e9
Instructions (Instant 600 s)	22.941e9	22.883e9
Peak footprint (Studio 180 s)	139.9 MB	139.8 MB
Peak footprint (Instant 600 s)	104.8 MB	106.3 MB

Confidence Score: 5/5

The PR appears safe to merge; the earlier open-file problem is fixed and no new blocking issues were found.

Summary

The PR runs audio finalization and checks alongside video work. The latest change fixes the earlier open-file finding.

• Instant recordings finalize audio while video work runs.
• Studio segments finish audio work alongside video.
• Recovered audio tracks are checked in parallel without changing error order.

_{Reviews (2) · Last reviewed commit: "fix(recording): join the Instant audio c..." · Reviewed by Greptile}

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Project	Deployment	Actions	Updated
cap-status	Ready	Preview	Oct 14, 2026 7:04pm UTC

[richiemcilroy]

hey @greptileai, please re-review the PR

[capy-ai]

Capy found no issues.

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