Kodi = LibreELEC = Openelec = SPMC (for android)= Kodibuntu (Linux)
With librelec on a microsd sd card, it will go straight to kodi where you can add movies & addons
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Juddery video might be your network connection, wifi will struggle to play HD movies
Where are you getting the movies from? Streaming from dodgy addons, could be the sources just have slow network connections.
You need to read the full instructions, but basically, download the correct img.gz file for you device. to a pc. There is a tool, sd creator which you can use.
I use rufus Rufus - Create bootable USB drives the easy way where it says iso, select dd, then burn the img.gz file to the sd card.
Remove the power cable, insert sd card into device, hold in reset button. there will be a tiny hole on the device, use a paperclip, while holding in, plug the power lead in, wait a few seconds, then you should see the LibreELEC logo.
The next time you boot, it will automatically boot to libreelec, if you remove the sd card, it will boot to android.