Sharing an Instagram video on Vine, a shortform video-sharing service, is not as trivial as it seems at first blush.
Instagram's app does not connect directly to Twitter-owned Vine and Facebook is doing a surprisingly good job clamping down on third-party apps which would permit users to reshare Instagram videos to Vine. A workaround solution involves downloading these videos to your device before they can be manually posted to Vine.
If you're jailbroken, there are many Cydia tweaks for saving Instagram media to an iPhone, such as InstaBetter, InstaEnhancer and InstaTools, to mention a few. In this tutorial, we'll be covering the process of resharing Instagram videos to Vine using InstaBoard for iPhone, a free app for downloading Instagram media to iOS devices.