Movie database browser
Your first if can be simplifed with any function.

function any ($list, $pred) 
{
     foreach ($list as $value) 
     {
          if (call_user_func ($pred, $value) == TRUE)
             return TRUE;
     }
     return FALSE;
}


So it will be :

 $toTest = [$_FILES['browseMovie'], 
            $_FILES['browseThumbnail'], 
            $_GET['title'], 
            $_GET['description'] ]
 if (any ($toTest, "empty")) die ("Please insert all fields")


Then you can simplify the code even more by creating a validate type function

function validateFile ($filePartsMovie, $filePartsThumbnail) 
{
      if($filePartsMovie['extension'] !== "mp4")
      {
           die('Video has to be a .mp4 file.');
      }

      if($filePartsThumbnail['extension'] !== "jpg" &amp;&amp;
         $filePartsThumbnail['extension'] !== "png")
      {
          die('Thumbnail has to be in jpg/jpeg or png format.');
      } 

     if($_FILES['browseMovie']['size'] + $_FILES['browseThumbnail']['size'] &gt; 1600600000)
     {
              die('filesize of video and thumbnail = higher 1.5 GB.');
     }
}


Then you can create a validate function for the rest of the code.

TLDR is to split your code in more separate functions.

BTW I think you do not need brackets when having only one statement after if.