Get a youtube video information from get_video_info.

getYoutubeVideoInfo.coffee

request = require 'request'

youTubeMovieInfo = 
  youTubeMovieId: 'videoId'

url = "http://www.youtube.com/get_video_info?video_id=#{youTubeMovieInfo.youTubeMovieId}"
request.get url, (err, res, body) ->
  return callback(false)  if err
  return callback(false)  if res.statusCode isnt 200

  formats = parseYoutubeInfoStringToFormats(body)
  return callback(false)  if formats is null

  mp4StreamUrl = getMp4StreamUrlFromFormats(formats)
  youTubeMovieInfo.mp4StreamUrl = mp4StreamUrl


# parse youtube api json response.
parseYoutubeInfoStringToFormats = (youtubeInfoString) -> 
  youtubeInfoArray = youtubeInfoString.split '&'
  
  return null if youtubeInfoArray[0] is 'status=fail'
  
  formatStreamArrayString = (element for element in youtubeInfoArray when element.split('=')[0] is 'url_encoded_fmt_stream_map')[0].split('=')[1]
  formatStreamArray = decodeURIComponent(formatStreamArrayString).split(',')
  
  formats = []
  for formatStreamString in formatStreamArray
    formatInfoArray = formatStreamString.split '&'
    
    formatInfoMap = {}
    for formatInfoElement in formatInfoArray
      formatInfoElementPair = formatInfoElement.split '='
      formatInfoMap[formatInfoElementPair[0]] = decodeURIComponent(formatInfoElementPair[1])
      
    formats.push formatInfoMap
    
  return formats
  

# find mp4 stream url from parsed data.
getMp4StreamUrlFromFormats = (formats) ->
  return format.url for format in formats when format.itag is '18'

How do I return the MP4 URL for download using PHP? My function is below:
`function getVideoInfo($video_id){

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, 'https://www.youtube.com/youtubei/v1/player?key=AIzaSyAO_FJ2SlqU8Q4STEHLGCilw_Y9_11qcW8');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, '{  "context": {    "client": {      "hl": "en",      "clientName": "WEB",      "clientVersion": "2.20210721.00.00",      "clientFormFactor": "UNKNOWN_FORM_FACTOR",   "clientScreen": "WATCH",      "mainAppWebInfo": {        "graftUrl": "/watch?v='.$video_id.'",           }    },    "user": {      "lockedSafetyMode": false    },    "request": {      "useSsl": true,      "internalExperimentFlags": [],      "consistencyTokenJars": []    }  },  "videoId": "'.$video_id.'",  "playbackContext": {    "contentPlaybackContext": {        "vis": 0,      "splay": false,      "autoCaptionsDefaultOn": false,      "autonavState": "STATE_NONE",      "html5Preference": "HTML5_PREF_WANTS",      "lactMilliseconds": "-1"    }  },  "racyCheckOk": false,  "contentCheckOk": false}');
curl_setopt($ch, CURLOPT_ENCODING, 'gzip, deflate');

$headers = array();
$headers[] = 'Content-Type: application/json';
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$result = curl_exec($ch);
if (curl_errno($ch)) {
    echo 'Error:' . curl_error($ch);
}
curl_close($ch);
return $result;

}

$video_link = 'https://www.youtube.com/watch?v='.$vid;
preg_match('%(?:youtube(?:-nocookie)?.com/(?:[^/]+/.+/|(?:v|e(?:mbed)?)/|.*[?&]v=)|youtu.be/)([^"&?/ ]{11})%i', $video_link, $match);
$video_id = $vid;
$video = json_decode(getVideoInfo($video_id));
$formats = $video->streamingData->formats;
$adaptiveFormats = $video->streamingData->adaptiveFormats;
$thumbnails = $video->videoDetails->thumbnail->thumbnails;
$title = $video->videoDetails->title;
$short_description = $video->videoDetails->shortDescription;
$thumbnail = end($thumbnails)->url;`