I received the adaptor and HDMI cable. However, after I opened the package, I realized that I had bought the wrong kind. This is called Digital AV adaptor, it is for ipad 2 and 3. Anyway, I tried it with a iPad 2 and it worked well. If you put the iPad horizontally, the screen is just a little bit narrower, but not bad. The one I bought was made by VicTsing, on Amazon, it costs $15.99 and a HDMI cable included, free shipping eligible. There are other cheaper versions, I picked this one because it has better customer rating. Some has very bad comments like not connecting steadily &etc.
I was pretty dumb, I bought the exact same kind as that kid named on Youtube, not realizing that he had iPad 2. Anyway, I Googled again - For iPad 4, I need Lightening Digital AV Adaptor. On Amazon, I only found Apple made, which costs $43.37 free shipping. If anyone know a cheaper version, please let me know. It shouldn't be that hard to make, right?