Answer first
A private Instagram video cannot be fetched just by pasting its URL into a transcript service. The post still requires the viewer's Instagram permission and an authenticated session. If you own the video or have permission to use it, download or export the file through an authorized workflow, then use Instagram Transcript to process that local file in the browser.
What is and is not possible
- A public URL may be supported by a service that explicitly fetches public media.
- A private URL is not a substitute for the video file; a tool should not ask you to bypass access controls.
- An MP4, MOV, WebM, M4A, MP3, or WAV file that you are allowed to use can be transcribed locally.
- Speech transcription will not recover words that exist only in a private post's on-screen stickers or slides. Those require a separate visual text workflow.
A privacy-conscious workflow
- Use Instagram's normal download or export option, or ask the owner for the original file.
- Open the local transcript tool and select the file from your device.
- Choose the spoken language when the clip is multilingual.
- Keep timestamps if you need to check names, numbers, or quotations against the source.
- Delete the local copy when your work is finished if it contains sensitive material.
Why private URLs often fail
The failure is usually an access problem, not a speech-recognition problem. A service without your authenticated Instagram session cannot see a private post, and giving a third party your login would create a separate security risk. A local file avoids that URL-access dependency while keeping the permission decision with you.
Final checklist
If you do not have the file or permission to use it, stop at the access boundary. If you do have an authorized copy, a local browser workflow can transcribe the spoken audio without uploading the video to a server.