$re = '/.*?(jmcs:.*?)".*/m';
$str = '"__class": "ContentAuthorizationEntry",
"duration": 300,
"changelist": 544216,
"urls": {
"jmcs://jd-contents/Sun/Sun_ULTRA.webm": "https://jd-s3.akamaized.net/private/map/Sun/Sun_ULTRA.webm/9c28826a30e2df0709aa023f3011d2ab.webm?auth=exp=16179930733600~acl=/private/map/Sun/*~hmac=5132987c51a3bcda04d7ef516a0d52af97acc530b65a25a6c9af1e508f1f9b4a",
..............
"jmcs://jd-contents/Sun/Sun.ogg": "https://jd-s3.akamaized.net/private/map/Sun/Sun.ogg/912779afd750760452be587dc7527d0f.ogg?auth=exp=16179930733600~acl=/private/map/Sun/*~hmac=5132987c51a3bcda04d7ef516a0d52af97acc530b65a25a6c9af1e508f1f9b4a"
}
}';
$subst = '$1';
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;