How to install VLC Player on the original iPad (iOS 5.1.1)?
version 2.2.x is what you need.

The latest with 5.1 support according to wiki:
https://wiki.videolan.org/Documentation:IOS/#Feature_Overview

Download away! Vlc keeps all the different versions!
http://downloads.videolan.org/videolan/vlc-iOS/

No Jailbreak required.