试图解析一个json

After getting a json from Youtube API. I used this code to parse it:

    $en = json_encode($json, true);
    echo "<pre>";
    print_r($en);
    echo "</pre>";

here is the result:

{"items":[{"id":"UC-D8SQfw-J-lSWFSbyX6wRg"}]}

I made it clear with an online json parser here's how it looks:

{

"items":[
    {
        "id":"UC-D8SQfw-J-lSWFSbyX6wRg"
    }
]

}

I want to get id value. I have tried $en->items->id but it says Notice: Trying to get property of non-object

how do I get the value of id ?

$en = json_encode($json, true);
$en_b = json_decode($en, true);
echo $en_b['items'][0]['id'];