Choose "Narrate a video" from the plus button beside Record. With that menu open, the U key picks it.
What you can upload
MP4, WebM, MOV or MKV, up to 50 GB. Drop the file onto the form or browse for it. Other kinds of file are refused with "Choose an MP4, WebM, MOV or MKV video."
While it uploads
The form shows "Checking source", then "Uploading" with a percentage, then "Verifying source…". Keep the page open until it finishes. "Pause upload" stops it on purpose.
If the upload stops
Select the same file again. The upload carries on from where it stopped and does not start from the beginning. If the connection is unreliable the app says so: "The connection keeps dropping. Select the same file again to resume from where it stopped."
A project whose upload stopped more than an hour ago is marked "Stalled". See A project stuck on "Transferring".
After the upload
In a cloud workspace, AI narration starts: the screens are found, a line is written for each, and the film is built. Your original file is kept. Pro and Studio include the narration. On Free it needs your own OpenAI and HeyGen keys. See OpenAI and HeyGen keys.
In the demo
The demo accepts files up to 20 GB and keeps them in your browser. It does not narrate.