how can i fetch the information from json youtube-dl when i use –get-id-open source projects rg3/youtube-dl

i have problem when i try to get the information from json file ($output) When i use youtube-dl . i need webpage_url from my json file my code is

$output = shell_exec('youtube-dl -J https://www.youtube.com/playlist?list=PLANMHOrJaFxPCjR2enLZBRgtZgjtXJ0MJ' );
$youtubeId = json_decode($output);
$youtubeId = $youtubeId->webpage_url;

echo $youtubeId;