About 18 hours in 512 MB is a storage calculation, not confirmation that ChatGPT accepts and processes an 18-hour recording.
An 18-hour recording sounds like a superpower. The catch: fitting inside the upload limit is not the same as being fully transcribed.
Storage estimate
At 64 kbps, 512 MB holds roughly 18 hours of MP3 audio; at 128 kbps, about nine; at 256 kbps, about four and a half. These are storage estimates, not processing promises.
Check the specific feature
The Files API allows 512 MB; the Transcriptions API allows 25 MB. Neither figure establishes the audio-attachment limit in ChatGPT. Check the formats and limits shown in your interface, then verify the result with a short test recording.
An upload confirmation is a ticket through the door, not a certificate that every minute was understood. Even the meeting attendees may not have managed that.
