Windows Codex dictation fails with "Unable to determine audio duration" and leaves retry state stuck

What version of the Codex App are you using (From “About Codex” dialog)?

26.715.9079.0

What subscription do you have?

ChatGPT paid individual subscription (signed in with ChatGPT; exact tier is not shown in the Codex About dialog)

What platform is your computer?

Microsoft Windows NT 10.0.19045.0 x64 (Windows 10 Pro 22H2, build 19045.7548)

What issue are you seeing?

Every short voice-dictation attempt in the Codex desktop app fails. No transcript is inserted, and the microphone button is replaced by circular retry arrows that can remain stuck. Local Codex logs record the following error twice for each attempt:

[Composer] dictation failed errorMessage="{\"detail\":\"Unable to determine audio duration\"}"

The same error occurred before and after updating Codex, and after using Windows Apps & features > ChatGPT > Advanced options > Repair.

What steps can reproduce the bug?

1. On Windows 10, open the Codex desktop app and focus the message composer.
2. Use Microsoft LifeCam Studio as the default recording device.
3. Start dictation, speak normally for approximately five seconds, and stop.
4. Observe that no text is inserted. The microphone becomes circular retry arrows.
5. Retry the dictation. The same error occurs.
6. Fully restart Codex or run the Windows App Repair action. The problem remains reproducible.

No special prompt, token usage, or context-window state is required; it also occurs after a fresh app restart.

What is the expected behavior?

Codex should accept a valid short microphone recording, transcribe it, and insert the resulting text. If transcription fails, the UI should show an actionable error and restore the microphone button instead of remaining in a stuck retry state.

Additional information

Hardware and Windows controls were tested separately:

• Microsoft LifeCam Studio is active and is the default recording endpoint.
• Capture level is 79% and the endpoint is not muted.
• A direct 10-second CoreAudio meter test recorded continuous activity (100/100 active samples; 17.3% maximum peak).
• Windows Voice Recorder created a valid 7.1-second M4A file (174,772 bytes), and the recorded voice was audible on playback.
• Windows Audio services are running.
• Windows microphone privacy is set to Allow, and Windows records Codex accessing the microphone during each attempt.
• Codex was updated from 26.715.7063.0 to 26.715.9079.0 and repaired through Windows Apps & features; neither changed the behavior.

This isolates the failure to the Codex dictation/audio-duration processing path rather than the microphone, driver, permissions, volume, or speakers. No recordings or private logs are attached.