As requested by a number of subscribers here is a very simple method of creating a Letter Box/Cinema Crop look for your youtube videos. This was done on Apple Final Cut Pro X but the same principle could be applied to almost any editing application, i.e. Premier, Vegas etc
Note that many applications like Premier and Final Cut have letter box function where you can simply apply the filter but having said that I've found on complicated timelines they usually fail somewhere. This is the only full proof way I've found that works for me.
Feel free to experiment with filters provided on your editing application as they may work for you. Hope this helps you spark some ideas in your next project.