I coded this project a while ago when I didn't really know what I was doing, and it breaks with a lot of edge-cases. I could fix it, or I could just tell you to use BrandonXLF/NBT.php which outputs data in the exact same format and actually works.
If you feel like fixing this one, feel free to make a pull request!
The Named Binary Tag file format is used by Minecraft to store data.
This class allows for simple reading of these files into an associative array.
After requiring nbt.php, it's a breeze to turn binary data into JSON:
$reader = new NBT;
$reader->loadString($data);
echo json_encode($reader->result);