Start from your Reel video file
Upload the original MP4, MOV or WebM. Use the file on your device rather than relying on an Instagram link; Instagram URL importing is still being verified.
Leave room for the interface
Use a vertical frame when appropriate. Put subtitles above the lower edge so they do not compete with the post description and account controls. Check placement in Instagram before posting.
Download a ready-to-upload MP4
Burned-in subtitles preserve the appearance in the video itself. Download the finished file, then publish it on Instagram. Connecting a publishing account is not required to download your export.