Как мне узнать, откуда появилась переменная arr?

Пожалуйста, найдите полный код здесь: Github / bitnol

Для справки проверьте это:

<?php

/**
* Author: Akhilesh Chandra Gupta
* Author URI: http://www.bitnol.com
* API URI: http://api.gitnol.com
* Description: Modular demo of the application of Cipher API
* License: MIT License
*/

// Video with cipher signature
$video_id = "zDrNLZ1uJ2w";
$results = getYTLink($video_id);
var_dump($results);

function getYTLink($video_id){

// get_video_info url formation
// although for cipher signature we have to get the details from the video's webapge not from get_video_info object
$info_url = "http://www.youtube.com/get_video_info?el=detailpage&asv=3&video_id=".$video_id;

// youtube webpage url formation
$yt_url = 'http://www.youtube.com/watch?v='.$video_id.'&gl=US&persist_gl=1&hl=en&persist_hl=1';;

// get the contents from the url
$raw_data = file_get_contents($info_url);

// parse the data received and save it as an array
$output = array();
parse_str($raw_data,$output);

// check the status of the get_video_info object
if($output['status']=='ok'){

// check for the cipher signature
$cipher = (isset($output['use_cipher_signature']) &&  $output['use_cipher_signature']=='True') ? true : false;

// If cipher is true then we have to decode it
if($cipher == true){

// if cipher is true then we have to change the plan and get the details from the video's youtube wbe page
$yt_html = file_get_contents($yt_url);

// parse for the script containing the configuration
preg_match('/ytplayer.config = {(.*?)};/',$yt_html,$match);
$yt_object = @json_decode('{'.$match[1].'}') ;

/// check if we are able to parse data
if(!is_object($yt_object)){
//'Sorry! Unable to parse Data';
return 'Error Code 1';
}else{

// parse available formats
$formats = $yt_object->args->url_encoded_fmt_stream_map;
// get the player id from assets section
$player_id = strbtwn($yt_object->assets->js,'html5player-','.js');
$player_id = explode("/", $player_id);
$player_id = $player_id[0];

// get the algo dictionary
// first check if the file exists
if(file_exists('./algo.json'))
$algos = json_decode(file_get_contents('algo.json'),true);
else{
// API call to fetch the algo dictionary
$algos_dict = file_get_contents("http://api.gitnol.com/getAlgo.php?playerID=".$player_id);

// saving the algo dictonary in local env for easy access
// Note: Developers should save the dictionary in their local env.
// Only make the API call for the new player ids which is not present in the algo dictionary.
// Repeated violation will results in IP ban.
file_put_contents('algo.json', $algos_dict);

$algos = json_decode($algos_dict,true);
}

/// check if the algo exist for the given player id
if(!array_key_exists($player_id, $algos)){

// if the algo dictionary is old then fetch a new one
$algos_dict = file_get_contents("http://api.gitnol.com/getAlgo.php?playerID=".$player_id);
file_put_contents('algo.json', $algos_dict);

$algos = json_decode($algos_dict,true);
$algo = $algos[$player_id][1];

}else{
$algo = $algos[$player_id][1];
}

// download links formation
$dlinks = array();
$links  = explode(',',$formats);foreach ($links as $link) {
parse_str($link,$linkarr);

// parse link array one by one and decrypt the signature
$dlinks[$linkarr['itag']] = $linkarr['url'] . "&signature=" . decrypt($linkarr['s'],$algo);
}
return $dlinks;
}

}else{
//'Video Is not cipher not needed to decode';
return 'Error Code 2';
}
}else{
//'Unable to get Video Info';
return 'Error Code 3';
}
}
// string helper function
function strbtwn($content,$start,$end){
$r = explode($start, $content);
if (isset($r[1])){
$r = explode($end, $r[1]);
return $r[0];
}
return '';
}

// signature decoding
// parse the python string operation into php string operation
function decrypt($sig,$algo){
$funcarr = explode(' + ', $algo);
$decrypt = '';
foreach($funcarr as $singfunc){
$singfunc = substr($singfunc,2,-1);
$operators = explode(':', $singfunc);
if (sizeof($operators) == 1) {
$decrypt .= $sig[$operators[0]];
}
if (sizeof($operators) == 2) {
if($operators[0] == ''){
$decrypt .= substr($sig, 0 ,$operators[1]);
}
if($operators[1] == ''){
$decrypt .= substr($sig, $operators[0]);
}
if($operators[0] >= 0 && $operators[1] >= 0){
$decrypt .= substr($sig, $operators[0], $operators[1] - $operators[0]);
}
}
if (sizeof($operators) == 3) {
if($operators[0] == '' && $operators[1] == ''){
$decrypt .= strrev($sig);
}
if($operators[0] >=0 && $operators[1] == ''){
$decrypt .= strrev(substr($sig, 0, $operators[0] + 1));
}
if($operators[0] >=0 && $operators[1] >= 0){
$decrypt .= strrev(substr($sig, $operators[1] + 1, $operators[0] - $operators[1]));
}
}
}
return $decrypt;
}
?>

Я думаю, что это решит вашу проблему.