This is a basic converter to turn vanilla minecraft player.dat files into Multiverse-Inventories .json files.
php convert.php player.dat player.json
PHP 5.3+ with the gmp extension.
Inventory, EnderChest contents, Armor
Everything else (XP, Health, Hunger, Bed spawn, etc)
Public domain. Attribution would be nice.
Utilizes the PHP NBT Decoder / Encoder library by Justin Martin frozenfire@thefrozenfire.com https://github.com/TheFrozenFire/PHP-NBT-Decoder-Encoder