DVD Half-Size Compression?

[odellkevin]

I recently bought a bunch of dvd's from street vendors in Kuwait. They are all pirates, I know, but anyway, the big draw is the fact that they usually put 4 or 5 movies on 1 disc, (ie, all the Rocky's, all the Terminator's, all the Aliens, etc) How do they fit them all? Well, firstly, they use dual layer dvd's (approx 8.? GB) But, sometimes, they also use an encoding/compression technique I've never seen. One disc had Dawn Of The Dead (2004) on it, it wasn't a camcorder rip, it was ripped from a dvd (don't ask me how they got one), the movie was 1 hour 40 minutes long, but it's final size on the dvd was only 990 MB and the image quality was very good. My question is, how did they get it so small? One thing I did notice (and they did this with several movies) was if you open the video_ts.ifo file directly off the disc into Media Player Classic, at 100% zoom, the picture is only 352 x 240, so it is half size (like what people do alot when making divx movies to reduce file size) but this is not divx, it is standard vobs, and when you play it back through a standard dvd player and tv, it shows up full screen full size, like a regular dvd. Has anyone ever heard of this or know how to do it? (Note: in the video info block, it says it is 704x480 60hz 4:3, but it is not, it is half that, and yes I am sure I have my playback set to 100%)

[Qyd]

Tmpgenc plus has a ntsc and pal "low resolution" (352x240 and 352x288 respectively) wizard that would encode at half frame. So i guess it's possible.
This would bring the total playing time from 155 to 245min.

ps: i guess this topic is not about copyright infridgement, but about techincal stuff.