processVideo is just a key to store it in your queue. You can name it whatever you want. 4871 is the id of the video. A simple example would be if you have a table in database that holds information about video files that needs to be processed:
Table columns
id, file_path, is_processed
When you upload a video file, you store the information in your video table, with flag is_processed = 0 , then you add the file to the queue
$video = new VideoModel();
$video->setFilePath('PATH_TO_VIDEO_FILE');
$video->setIsProcessed(0);
$video->save();
// $video->getId() will give you the id (in the above example 4871)
$queue->put(array('processVideo' => $video->getId()));