Video. Slice & Save
Create longs stories for instagram.
Select video, application splits video into equitably chunks, auto-generate subtitles and save it back to gallery.
Without lost video, simple UI to do it easy.
You can change chunk duration from 1 sec up to 15 minutes
standard Apple Terms of Use (EULA):
https://www.apple.com/legal/internet-services/itunes/dev/stdeula/