in which video format does hard disk camera stores video?..for how many hours we can record in dvd?

The price should tell you. You get what you pay for! On the other hand, I will give you the tech answer. On the DVD cameras, you are dealing with a spinning disk that is recording data, therefore the data will be recorded at a slower rate than a hard drive depending on the price and model you purchase. If you bump a DVD recorder then you will get a skip in your video vise a hard drive recorder will not because the data is going strait to the hard drive. With a DVD recorder you have to contend with "what DVD is best with my recorder" vise having the same recording media all the time. Last the DVD needs to finalize the disk in the end of recording and the Hardrive does not. You could loose that important moment when the disk is finalizing itself. I would like to reemphasize that in the electronic world you get what you pay for and I have had very few times when a bargain is a bargain in the electronic world.Good Luck!

Without going on detailed explanation, I can tell that Hard Disk (HDD) cameras are the better between these two, but the price is more. Both the cameras (HDD and DVD disk) uses MPEG-2 formats. For DVD disk cameras you can use mini DVD disks. These can normally record about 30 minutes (the best quality movie), but you can get more recording time, if you don't use the best movie quality. For HDD cameras your recording time depend upon the movie quality you select and the capacity of the Hard Disk. Normaly with a 30 GB camera you will be able to record 7 and a half hour at the best quality (more than 10 hours at a lower quality- which I think will satisfy your required quality).