dd stalls on some dvd's

[mousemurder]

hi, my acer revo nettop doesnt have a dvd drive so i have to rip stuff to my network in order to view them. i do:
lsdvd && dd if=dev/dvd of=moo-vee.iso
i got star-trek but it freezes at 25mb (i think where vts_3_1.vob begins -- the main film).

why does this happen, i thought dd was supposed to create a byte-for-byte replica of the content on the dvd ?

[nm]

Maybe there are corrupted sectors on the disc because of ARccOS (http://en.wikipedia.org/wiki/ARccOS_Protection) or some similar copy protection scheme.

You can try gddrescue or dd_rescue: http://www.gentoo-wiki.info/HOWTO_Backup_a_DVD#ARccOS_.26_Other_intentional_sector_corruption

Or run some Windows ripping tool with Wine.

[mousemurder]

^ thanks, the 2nd link helps a lot. now i kinda' get it.
i actually used vobcopy -b 25m to skip the first 25 megabytes but no menus.

[microchip8]

I found ddrescue works better on such discs

[Dinominant]

I usually use dd and simply replace bad blocks with null since they contain garbage anyway
filestat /dev/dvd && dd if=/dev/dvd bs=2048 conv=noerror,sync of="dvd.iso"