I came across the following tips on How to create professional looking video previews on instagram that may be of some help. Good luck with it.
How to create your own advanced Instagram video preview with text/images/motion:
1. 1Edit together your 14 second sequence on a custom 640×640 timeline.
2. Add text, photos or a video wrapper to your timeline.
3. Export the video at 640×640 resolution, .MOV file format and H.264 compression.
4. Place the video file in your dropbox folder or email yourself the file.
5. Save the video file inside dropbox or your Mail app to your camera roll.
6. Upload video to Instagram.
How to create your own basic Instagram video preview with simple white/black bars:
1. Edit together your 14 second sequence on a 16×9 aspect ratio timeline.
2. Export the video at native resolution, .MOV file format and H.264 compression.
3. Place the video file in your dropbox folder or email yourself the file.
4. Save the video file inside dropbox or your Mail app to your camera roll.
5. Edit video within SquareadyV app (iOS) or Video Squarer (Android)