{"v": 50, "vd": 5},
{"v": 51, "vd": 1},
{"v": 54, "vd": 3},
{"v": 57, "vd": 3},
{"v": 60, "vd": 3},
{"v": 61, "vd": 1},
{"v": 62, "vd": 1},
{"v": 63, "vd": 1},
{"v": 63, "vd": 0},
$result = implode(',', array_column(json_decode($str, true), 'v'));
preg_match_all('~(?<="v": )\d+~', $str, $match);
$result = implode(',', $match[0]);
$json = '{"v": 50, "vd": 5},
{"v": 51, "vd": 1},
{"v": 54, "vd": 3},
{"v": 57, "vd": 3},
{"v": 60, "vd": 3},
{"v": 61, "vd": 1},
{"v": 62, "vd": 1},
{"v": 63, "vd": 1},
{"v": 63, "vd": 0}';
$array = array_map(function($a){ return $a['v']; }, json_decode("[$json]", true));
var_dump($array);