I was able to get the upload working using the following code:

if($client->getAccessToken()) {
    $snippet = new Google_VideoSnippet();
    $snippet->setTitle("Test title");
    $snippet->setDescription("Test descrition");
    $snippet->setTags(array("tag1","tag2"));
    $snippet->setCategoryId("22");

    $status = new Google_VideoStatus();
    $status->privacyStatus = "private";

    $video = new Google_Video();
    $video->setSnippet($snippet);
    $video->setStatus($status);

    $error = true;
    $i = 0;

    try {
        $obj = $youTubeService->videos->insert("status,snippet", $video,
                                         array("data"=>file_get_contents("video.mp4"), 
                                        "mimeType" => "video/mp4"));
    } catch(Google_ServiceException $e) {
        print "Caught Google service Exception ".$e->getCode(). " message is ".$e->getMessage(). " <br>";
        print "Stack trace is ".$e->getTraceAsString();
    }
}

You can use the following code to upload the file just after user has signin when user click a submit button with the path defined in a text input :

<?php
/**
 * Library Requirements
 *
 * 1. Install composer (https://getcomposer.org)
 * 2. On the command line, change to this directory (api-samples/php)
 * 3. Require the google/apiclient library
 *    $ composer require google/apiclient:~2.0
 */
if (!file_exists(__DIR__ . '/vendor/autoload.php')) {
  throw new \Exception('please run "composer require google/apiclient:~2.0" in "' . __DIR__ .'"');
}
require_once __DIR__ . '/vendor/autoload.php';
session_start();

$response = "";

/*
 * You can acquire an OAuth 2.0 client ID and client secret from the
 * {{ Google Cloud Console }} <{{ https://cloud.google.com/console }}>
 * For more information about using OAuth 2.0 to access Google APIs, please see:
 * <https://developers.google.com/youtube/v3/guides/authentication>
 * Please ensure that you have enabled the YouTube Data API for your project.
 */
$OAUTH2_CLIENT_ID = 'YOUR_CLIENTID';
$OAUTH2_CLIENT_SECRET = 'YOUR_CLIENT_SECRET';

$client = new Google_Client();
$client->setClientId($OAUTH2_CLIENT_ID);
$client->setClientSecret($OAUTH2_CLIENT_SECRET);
$client->setScopes('https://www.googleapis.com/auth/youtube');

$redirect = filter_var('http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'],
    FILTER_SANITIZE_URL);

$client->setRedirectUri($redirect);
// Define an object that will be used to make all API requests.
$youtube = new Google_Service_YouTube($client);
// Check if an auth token exists for the required scopes
$tokenSessionKey = 'token-' . $client->prepareScopes();
if (isset($_GET['code'])) {
  if (strval($_SESSION['state']) !== strval($_GET['state'])) {
    die('The session state did not match.');
  }
  $client->authenticate($_GET['code']);
  $_SESSION[$tokenSessionKey] = $client->getAccessToken();
  header('Location: ' . $redirect);
}
if (isset($_SESSION[$tokenSessionKey])) {
  $client->setAccessToken($_SESSION[$tokenSessionKey]);
}
// Check to ensure that the access token was successfully acquired.

if ($client->getAccessToken()) {
  try {

    $videoPath = "";

    if (isset($_GET['videoPath'])){
    $videoPath = $_GET['videoPath'];
    }
    else if(isset($_SESSION['videoPath'])){
      $videoPath = $_SESSION['videoPath'];
    }

    if(isset($videoPath) && !isset($_GET['state']) && file_exists($videoPath)) {

      // Create a snippet with title, description, tags and category ID
      // Create an asset resource and set its snippet metadata and type.
      // This example sets the video's title, description, keyword tags, and
      // video category.
      $snippet = new Google_Service_YouTube_VideoSnippet();
      $snippet->setTitle("Test title");
      $snippet->setDescription("Test description");
      $snippet->setTags(array("tag1", "tag2"));

      // Numeric video category. See
      // https://developers.google.com/youtube/v3/docs/videoCategories/list
      $snippet->setCategoryId("22");

      // Set the video's status to "public". Valid statuses are "public",
      // "private" and "unlisted".
      $status = new Google_Service_YouTube_VideoStatus();
      $status->privacyStatus = "private";

      // Associate the snippet and status objects with a new video resource.
      $video = new Google_Service_YouTube_Video();
      $video->setSnippet($snippet);
      $video->setStatus($status);

      // Specify the size of each chunk of data, in bytes. Set a higher value for
      // reliable connection as fewer chunks lead to faster uploads. Set a lower
      // value for better recovery on less reliable connections.
      $chunkSizeBytes = 1 * 1024 * 1024;

      // Setting the defer flag to true tells the client to return a request which can be called
      // with ->execute(); instead of making the API call immediately.
      $client->setDefer(true);

      // Create a request for the API's videos.insert method to create and upload the video.
      $insertRequest = $youtube->videos->insert("status,snippet", $video);

      // Create a MediaFileUpload object for resumable uploads.
      $media = new Google_Http_MediaFileUpload(
          $client,
          $insertRequest,
          'video/*',
          null,
          true,
          $chunkSizeBytes
      );
      $media->setFileSize(filesize($videoPath));

      // Read the media file and upload it chunk by chunk.
      $status = false;
      $handle = fopen($videoPath, "rb");
      while (!$status && !feof($handle)) {
        $chunk = fread($handle, $chunkSizeBytes);
        $status = $media->nextChunk($chunk);
      }

      fclose($handle);

      // If you want to make other calls after the file upload, set setDefer back to false
      $client->setDefer(false);

      $response .= "<h3>Video Uploaded</h3><ul>";
      $response .= sprintf('<li>%s (%s)</li>',
          $status['snippet']['title'],
          $status['id']);

      $response .= '</ul>';

      $_SESSION['path'] = "";
  }
  else{
    $response = "no path was specified or file doesn't exist";
    file_put_contents('php://stderr', print_r("no path was specified or file doesn't exist", TRUE));
  }

  } catch (Google_Service_Exception $e) {
    $response = htmlspecialchars($e->getMessage());
  } catch (Google_Exception $e) {
    $response = htmlspecialchars($e->getMessage());
  }
  $_SESSION[$tokenSessionKey] = $client->getAccessToken();
} else {

  if(isset($_GET['videoPath'])){

    $_SESSION["videoPath"] = $_GET['videoPath'];

    // If the user hasn't authorized the app, initiate the OAuth flow
    $state = mt_rand();
    $client->setState($state);
    $_SESSION['state'] = $state;
    $authUrl = $client->createAuthUrl();
    header('Location: ' . $authUrl);
  }
}
?>

<!doctype html>
<html>
<head>
 <title>Upload Video</title>
</head>
<body>
   <div>
        <form id="form" action="resumable_upload.php"">

          <label>Enter the path to the video to upload
           :
                <input id="video-path" name="videoPath" value='/path/to/video' type="text" />
          </label>
          <input name="action" type="submit" value="Upload video" />
        </form>
        <div id="playlist-container">
          <?php echo $response ?>
        </div>
    </div>
</body>
</html>

But if the page gets refreshed or if the user clicks the button by mistake one more time, it will re-upload the video. Check this post to deal with the duplicated video issue

I think I found the answer from this article.

Steps:

Step 1. Create a token.php (make sure set it to 777). Place the code example from Google - https://developers.google.com/youtube/v3/code_samples/php#upload_a_video - with a little of this modification as follow:

Change:

if (isset($_SESSION['token'])) {
  $client->setAccessToken($_SESSION['token']);
}

To:

if (isset($_SESSION['token'])) {
  $client->setAccessToken($_SESSION['token']);

  // @ref: http://www.whitewareweb.com/php-youtube-video-upload-google-api-oauth-2-0-v3/
  echo "Access Token: " . $_SESSION['token'];
}

Step 2. Run token.php on your browser. Grant the access. Then you get a json output below:

{
  "access_token": "xxxxt7YvjObwYx3DG4NRmfjiQ",
  "token_type": "Bearer",
  "expires_in": 3600,
  "refresh_token": "xxxxq5hzQTUapZ7zyRIHP7X_G8",
  "created": 1466238624
}

Save it as token.txt

Step 3. Create upload.php with the same example code from Google - with the following modification:

One. Include token.txt file in the beginning of your upload.php:

$key = file_get_contents('token.txt');

Then pass $key into new Google_Client():

$OAUTH2_CLIENT_ID = 'xxxx.googleusercontent.com';
$OAUTH2_CLIENT_SECRET = 'xxxx';

// Client init
$client = new Google_Client();
$client->setClientId($OAUTH2_CLIENT_ID);
$client->setAccessType('offline');
$client->setApprovalPrompt('force');
$client->setAccessToken($key);
$client->setClientSecret($OAUTH2_CLIENT_SECRET);

Two. Add this code in the try catch section before $youtube = new Google_Service_YouTube($client);:

    /**
     * Check to see if our access token has expired. If so, get a new one and save it to file for future use.
     */
    if($client->isAccessTokenExpired()) {
        $newToken = json_decode($client->getAccessToken());
        $client->refreshToken($newToken->refresh_token);
        file_put_contents('token.txt', $client->getAccessToken());
    }

Step 4. Run upload.php that's it.

You can get the entire code from that article.

There's now support for resumable uploads using CORS in the YouTube Data API v3.

A rough, but working, example at https://youtube-api-samples.googlecode.com/git/yt-upload-javascript/index.html (source files at https://code.google.com/p/youtube-api-samples/source/browse/#git%2Fyt-upload-javascript) that shows the upload flow, using the Google+ sign-in button to handle OAuth 2 (you can use the normal OAuth 2 browser client flow if you'd prefer) and with a progress indicator. It also shows how you could poll for video processing status following an upload and embed the resulting video on a page once it's been processed.

Here is my code with Zend

    //include Zend Gdata Libs

require_once("Zend/Gdata/ClientLogin.php");       
require_once("Zend/Gdata/HttpClient.php");          
require_once("Zend/Gdata/YouTube.php");          
require_once("Zend/Gdata/App/HttpException.php");         
require_once('Zend/Uri/Http.php');

//yt account info
$yt_user = '[email protected]'; //youtube username or gmail account
$yt_pw = 'mypassword'; //account password
$yt_source = 'title of my video'; //name of application (can be anything)

//yt dev key  get here : https://code.google.com/apis/youtube/dashboard/
$yt_api_key = ''ABC123 ... ''; //your youtube developer key

//login in to YT
$authenticationURL= 'https://www.google.com/youtube/accounts/ClientLogin';
$httpClient = Zend_Gdata_ClientLogin::getHttpClient(
                                          $username = $yt_user,
                                          $password = $yt_pw,
                                          $service = 'youtube',
                                          $client = null,
                                          $source = $yt_source, // a short string identifying your application
                                          $loginToken = null,
                                          $loginCaptcha = null,
                                          $authenticationURL);

// Note that this example creates an unversioned service object.
// You do not need to specify a version number to upload content
// since the upload behavior is the same for all API versions.
//$yt = new Zend_Gdata_YouTube($httpClient);
$yt = new Zend_Gdata_YouTube($httpClient, $yt_source, NULL, $yt_api_key);

I can Upload my file and after a while I'm redirected to "$nextUrl". My issue is that I get this page : http://www.example.com/youtube_uploads?statu=400&error=failed And I don't no why.

Any Idea, please ?

Strangely a very small tweak in code fixes the problem.

Instead of just $videoPath = "/path/to/file.mp4"; using DOCUMENT_ROOT solves the issue. Other than that code of documentation is perfect.

$videoPath = $_SERVER["DOCUMENT_ROOT"] . "/mapapp/videos/test.mp4";