What I can find online is all about retrieving information from Vine (through undocumented APIs). How can I upload the video in my app to Vine programmatically?
I just found this app can do this on the app store:
https://itunes.apple.com/us/app/vinyet/id697065371
"For the first time, capture, enhance, and post your videos DIRECTLY to Vine or Instagram."
I found this: https://github.com/VineAPI/VineAPI/blob/master/endpoints.md
You need to use these requests: Login, Upload thumbnail, Upload video, Create post.
I don't know if it works or not, you have to try. In any case, the use of undocumented (private) API can lead to bad consequences.