Some surprise while "dd-ing" a video DVD...

Phillip Susi psusi at
Wed Jan 18 15:27:22 UTC 2006

Andrea Giuliano wrote:
> I know that a video DVD has an ISO9660 filesystem, just like any data 
> DVD or CD (if I'm not wrong). So I thought I could create an ISO image 
> of a video DVD using "dd" or "readcd", for instance.

DVDs use the UDF filesystem, no iso9660.  You can burn your own DVD with 
an iso filesystem on it, and I believe you have to if you want it to be 
bootable, but commercial DVDs use UDF.

> But "dd" issues an "input/output error" after a few seconds, and so does 
> "readcd". I thought this could be due to the encryption used on video 
> DVDs, but Nautilus can mount video DVD without problems, how can it do 
> that?

Yes, the disc is encrypted and to mount it, it must be unlocked. 
Nautilus does this automatically.

> Then, the solution came by itself: I just viewed a few seconds of the 
> DVD with "mplayer", then tried again with "dd" and... voilà, "dd" goes 
> on and on till all the ISO image is copied on my hard drive (a few hours 
> later...). I did all the above absolutely without any intention, I just 
> noticed that it worked!
> What did "mplayer" do that allowed "dd" to work?

It unlocked the disk, which means it sent the drive a valid key to 
decrypt the encrypted blocks.

> You have to know that:
> 1) all this happens with several different video DVDs;
> 2) the DVD drive is rather new (August 2005);
> 3) the disks work perfectly on my DVD player (I mean, they are original, 
> not copies, they are clean, they have no scratches, and so on)
> 4) I run Breezy, updated.
> Best regards.

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