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

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

Andrea Giuliano
Hi!

I'm doing some practice with video DVDs, and after some experiments I'm
now able to make divx with dvd::rip, or even with transcode without
serious problems. I post this just because I was curious about the ways
to dump video DVDs on hard disk at a lower level, and I ran across some
strange behaviour I cannot explain by myself.

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.

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?

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?

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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ICCU - Istituto Centrale per il Catalogo Unico
Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302

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

Joyce Markoll
Andrea Giuliano a écrit :
> Hi!
Hello,

> What did "mplayer" do that allowed "dd" to work?
Why do you want to attribute the better result do mplayer ? no sense to
that.
I also get regularly awful I/O errors on diverse operations with the CD
and DVD devices, be it burning, or else, such as ripping, but there is
no clue till here. It's mystic, I was advised to put garlic on the
machine :rolleyes!:

> 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.
If someone has clues, or if you find out what the trouble comes from,
I'd be
most interested, as I did search quite long, with diverses graphical
frontends, with tools in the shell, and on the web too.(CD and DVD are
close cousins, aren't they ?)
Greetings, Joyce Markoll.


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

hentaidan
In reply to this post by Andrea Giuliano
On 18/01/06, Andrea Giuliano <[hidden email]> wrote:
> Hi!
> 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.

According to http://www.burnworld.com/dvd/primer/filesystem.htm :

"DVD-Video discs use only UDF with all required data specified by UDF
and ISO 13346 to allow playing in computer systems. They do not use
ISO 9660 at all."

Never had any problems myself with dd on DVD's, though i've only tried
it with  Mac OS X disc. I use:

umount /dev/hdc
dd if=/dev/cdrom of=cd.iso

Dan
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Re: Some surprise while "dd-ing" a video DVD...

Andrea Giuliano
In reply to this post by Joyce Markoll
J.Markoll wrote:
>>What did "mplayer" do that allowed "dd" to work?
>
> Why do you want to attribute the better result do mplayer ? no sense to
> that.

I definitely agree with you, it's mystic, but it works. Why? I don't
know. Why mplayer? I know this one: I just tried with it, and the next
test will be with another DVD player. Would you bet on the result?

> I also get regularly awful I/O errors on diverse operations with the CD
> and DVD devices, be it burning, or else, such as ripping, but there is
> no clue till here. It's mystic, I was advised to put garlic on the
> machine :rolleyes!:

I prefer garlic with olive oil on spaghetti, but I will give a try to
your suggestion anyway.

Seriously, I get the same error in many other circumstances, but this is
a quite particular situation: sometimes the disks are not clean,
sometimes the drive quality is rather poor... but this time the only
difference I see is that every clean, well burned and scratch-free data
DVD can be dd-ed without problems on my drive, while the only way to
accomplish the same with video DVDs is following the above mystic receipt.

BTW, try to copy a video DVD with Nautilus/Copy Disc: I always get the
"No media available" error message, while it never happens with data
DVDs. I don't know if this has some relationship with the subject.

>
>
>>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.
>
> If someone has clues, or if you find out what the trouble comes from,
> I'd be
> most interested, as I did search quite long, with diverses graphical
> frontends, with tools in the shell, and on the web too.

Don't tell me about that! I've been spending several evenings this way,
and never found anything...

(CD and DVD are
> close cousins, aren't they ?)

I used to think so. Usually, you can simply mount a video DVD as an
ISO9660 filesystem. Then you can crawl in it anyway you want. I've
always thought that VOB files are encrypted, but not the ISO image. In
the latter case, it would be impossible to mount the DVD, I guess.

Anyway, thanks for your reply.

> Greetings, Joyce Markoll.
>

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ICCU - Istituto Centrale per il Catalogo Unico
Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302

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

Andrea Giuliano
In reply to this post by hentaidan
dan wrote:

> On 18/01/06, Andrea Giuliano <[hidden email]> wrote:
>
>>Hi!
>>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.
>
>
> According to http://www.burnworld.com/dvd/primer/filesystem.htm :
>
> "DVD-Video discs use only UDF with all required data specified by UDF
> and ISO 13346 to allow playing in computer systems. They do not use
> ISO 9660 at all."

So I was completely wrong: video DVDs use UDF, not ISO9660. I will try
to mount the image I dd-ed last night, and let you know (I have it at
home, I'm not home at present).

>
> Never had any problems myself with dd on DVD's, though i've only tried
> it with  Mac OS X disc. I use:
>
> umount /dev/hdc
> dd if=/dev/cdrom of=cd.iso
>

I guess you mean the disk used to install the operating system. I also
guess it's not a video DVD, that's right? If so, I think I could do the
same too. I tried to dd Debian DVD, Fedora DVD and a couple of other
data DVDs I burned, and they all work perfectly.

Again, the problem only seems to arise with video DVD.

Best regards.

> Dan
> --
> http://www.danicity.co.uk
>

--
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Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302

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

Phillip Susi
In reply to this post by Andrea Giuliano
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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Re: Some surprise while "dd-ing" a video DVD...

Joyce Markoll
In reply to this post by Andrea Giuliano
Andrea Giuliano a écrit :
> J.Markoll wrote:
>
>>> What did "mplayer" do that allowed "dd" to work?
[...]
> I used to think so. Usually, you can simply mount a video DVD as an
> ISO9660 filesystem. Then you can crawl in it anyway you want. I've
> always thought that VOB files are encrypted, but not the ISO image. In
> the latter case, it would be impossible to mount the DVD, I guess.
> Anyway, thanks for your reply.
Welcome
But forget about mplayer, about the garlic, and rather keep the eyes
upon Dan's answer. :)
Plus see the brand of DVD's (made).
Otherwise, see diverse softwares to do all kinds of things with DVD's.
I don't burn DVD's myself. Plus I'm also going to lower burning CD's,
as it's increasing the amount of waste.

=-=-=-=-=
 >> Acidrip:
 >> http://sourceforge.net/projects/acidrip/

Excellent pour ripper les DVD, frontend graphique pour mencoder. Mieux vaut
avoir lu "man mencoder" avant, toutefois... (bizarrement, ma petite formule
utilise elle aussi mencoder  ;-)
...mais

 >> Complément pour copier des DVD sous Linux:
 >> http://k9copy.free.fr/
=-=-=-=-=

If you wish to see further, you could browse the applications database.
Greetings, Joyce Markoll.



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

Arne Caspari-2
In reply to this post by Phillip Susi
Phillip Susi wrote:
> It unlocked the disk, which means it sent the drive a valid key to
> decrypt the encrypted blocks.

Correct me if I am wrong but AFAIK not the disc is encrypted but only
the video .VOB files.

So in my optinion, dd should work :-/


  /Arne

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

Arne Caspari-2
In reply to this post by Andrea Giuliano
Andrea,

try to extract the DVD image with "dvdisaster", to be found here:

http://www.dvdisaster.com/


  /Arne

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

hentaidan
In reply to this post by Andrea Giuliano
On 18/01/06, Andrea Giuliano <[hidden email]> wrote:

> dan wrote:
>
> >
> > Never had any problems myself with dd on DVD's, though i've only tried
> > it with  Mac OS X disc. I use:
> >
> > umount /dev/hdc
> > dd if=/dev/cdrom of=cd.iso
> >
>
> I guess you mean the disk used to install the operating system. I also
> guess it's not a video DVD, that's right? If so, I think I could do the
> same too. I tried to dd Debian DVD, Fedora DVD and a couple of other
> data DVDs I burned, and they all work perfectly.
>
> Again, the problem only seems to arise with video DVD.

Yes, sorry it was the install disc (I guess) a data disc. I also tried
to dd a video dvd (Pirates of the Cari.) and it seemed to be fine for
~200Mb (I Ctrl-C'd it). Though it might have been Nauty unlocking it
before hand as Philip suggested. I killed all nautilus processes and
unmounting etc. and it still seemed to work.

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

Noah Dain
On 1/18/06, dan <[hidden email]> wrote:

> On 18/01/06, Andrea Giuliano <[hidden email]> wrote:
> > dan wrote:
> >
> > >
> > > Never had any problems myself with dd on DVD's, though i've only tried
> > > it with  Mac OS X disc. I use:
> > >
> > > umount /dev/hdc
> > > dd if=/dev/cdrom of=cd.iso
> > >
> >
> > I guess you mean the disk used to install the operating system. I also
> > guess it's not a video DVD, that's right? If so, I think I could do the
> > same too. I tried to dd Debian DVD, Fedora DVD and a couple of other
> > data DVDs I burned, and they all work perfectly.
> >
> > Again, the problem only seems to arise with video DVD.
>
> Yes, sorry it was the install disc (I guess) a data disc. I also tried
> to dd a video dvd (Pirates of the Cari.) and it seemed to be fine for
> ~200Mb (I Ctrl-C'd it). Though it might have been Nauty unlocking it
> before hand as Philip suggested. I killed all nautilus processes and
> unmounting etc. and it still seemed to work.
>
> --
> http://www.danicity.co.uk
>
> --
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>

I work a lot with cd/dvd/floppy images and dd aborting is so common, I
have to mark it as "normal".

when dd is run in it's default form (dd if=xxx of=xxx), it will abort
on the first error it encounters resulting in 'input/output' error.
This is to avoid copying bad data.

resolution:  everytime i've run into this problem, baring a bad disk,
backing off on the drive speed has solved the problem.  You can set
this with "hdparm -E <cdrom speed>".  Note that this is not dvd speed.
 I usually start with something like 24 and back down from there if
necessary (20, 16, 12).

Also note that this process is NOT good for attempting to get an image
of a damaged cd/dvd.  As soon as dd hits an error, it still exits.
But, there are arguments to use to alter this behaviour:

basic recovery syntax:
  dd if=/dev/hdc of=file.txt conv=noerror,sync

  conv=noerror,sync - do not fail on errors and write zeros to
destination sectors with cannot be read

I don't know what this has to do with udf as all the dvd's i've seen
are iso9660 filesystem, or at least compatible with it.  The linux
kernel hasn't even had udf support for all that long now, and write
support is still experimental.  I know udf is used for packet writing,
where an optical disk is used read and write like one would a normal
harddisk.  I don't too much about the specifics, but this guy seems to
have done his homework:
http://www.mrichter.com/cdr/primer/udf.htm

As far as encryption on dvds go, the dvd itself isn't encrypted, just
the .vob files on it.  So, if you can't see the VIDEO_TS directory
with .vob (mpeg) files in it, then the problem is not with normal dvd
encryption.

and if all else fails, escalate to dd_rescue.


--
Noah Dain
"Single failures can occur for a variety of reasons that have nothing
to do with a hardware defect, such as cosmic radiation ..." - IBM
Thinkpad R40 maintenance manual, page 25

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

Phillip Susi
Noah Dain wrote:

> Also note that this process is NOT good for attempting to get an image
> of a damaged cd/dvd.  As soon as dd hits an error, it still exits.
> But, there are arguments to use to alter this behaviour:
>
> basic recovery syntax:
>   dd if=/dev/hdc of=file.txt conv=noerror,sync
>
>   conv=noerror,sync - do not fail on errors and write zeros to
> destination sectors with cannot be read
>


Of course, this will result in a partially broken image because the
parts that failed to read will be filled with zeros not the correct data.


> I don't know what this has to do with udf as all the dvd's i've seen
> are iso9660 filesystem, or at least compatible with it.  The linux
> kernel hasn't even had udf support for all that long now, and write
> support is still experimental.  I know udf is used for packet writing,
> where an optical disk is used read and write like one would a normal
> harddisk.  I don't too much about the specifics, but this guy seems to
> have done his homework:
> http://www.mrichter.com/cdr/primer/udf.htm
>


All commercial video DVDs use UDF, not iso9660.  The linux kernel has
supported UDF for several years, which is as long as it has supported
DVDs.

As for packet writing, I'm actually in the process right now of
improving the udftools package and fixing some bugs in the kernel to get
support for this fully integrated into ubuntu in a plug and play way.
See https://wiki.ubuntu.com/PacketCD


> As far as encryption on dvds go, the dvd itself isn't encrypted, just
> the .vob files on it.  So, if you can't see the VIDEO_TS directory
> with .vob (mpeg) files in it, then the problem is not with normal dvd
> encryption.
>

Actually, the DVD itelf _is_ encrypted, just not the whole thing.  The
sectors that contain the vob files are encrypted at the hardware level,
which is why dd can not read them.  The drive itself performs the
decryption of those sectors once it has been unlocked.  If the data file
itself were encrypted, then you would still be able to read and copy the
file even though you could not understand it's contents.



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

Andrea Giuliano
In reply to this post by Arne Caspari-2
Sure I'll try it, but please note that I just want to understand the
circumstances under which dd works or not. I already can copy DVD to
DivX, VCD and such in a quite satisfactory way. Nevertheless, I thank
you for your suggestion, another tool in my box is always welcome!

Best regards.

Arne Caspari wrote:
> Andrea,
>
> try to extract the DVD image with "dvdisaster", to be found here:
>
> http://www.dvdisaster.com/
>
>
>  /Arne
>

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Viale Castro Pretorio 105, Rome - ITALY
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Re: Some surprise while "dd-ing" a video DVD...

Andrea Giuliano
In reply to this post by Phillip Susi
First of all, thanks for you useful explanation.

> All commercial video DVDs use UDF, not iso9660.  The linux kernel has
> supported UDF for several years, which is as long as it has supported DVDs.

I believe in what you say, but actually I can mount a video DVD both as
UDF and ISO9660. As you say, Nautilus and "mount" unlock the DVD before
mount it, that's why I always can mount it.

Yet, I don't understand why dd should not copy a stream of byte from a
device if they represent an encrypted video DVD. I mean, whatever the
bytes represents, dd should dump them. At most, you should get a big,
useless file, but that file should be exactly what was written on the media.

But probably there's something I don't know. You said that mplayer (and
obviously xine, vlc and so on) unlocks the drive, and I guess you mean
"at the hardware level". If it's so, every tools like dd, tar, cpio and
such should fail reading the media.

Am I right?

Another question: is there something one can do before invoking dd to
accomplish the same without using mplayer? I have nothing against
mplayer, it's just curiousity.

Best regards.

>
> As for packet writing, I'm actually in the process right now of
> improving the udftools package and fixing some bugs in the kernel to get
> support for this fully integrated into ubuntu in a plug and play way.
> See https://wiki.ubuntu.com/PacketCD
>
>
>> As far as encryption on dvds go, the dvd itself isn't encrypted, just
>> the .vob files on it.  So, if you can't see the VIDEO_TS directory
>> with .vob (mpeg) files in it, then the problem is not with normal dvd
>> encryption.
>>
>
> Actually, the DVD itelf _is_ encrypted, just not the whole thing.  The
> sectors that contain the vob files are encrypted at the hardware level,
> which is why dd can not read them.  The drive itself performs the
> decryption of those sectors once it has been unlocked.  If the data file
> itself were encrypted, then you would still be able to read and copy the
> file even though you could not understand it's contents.
>
>
>

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

Nancy Rudins
On Thu, 19 Jan 2006, Andrea Giuliano wrote:

> First of all, thanks for you useful explanation.
>
> > All commercial video DVDs use UDF, not iso9660.  The linux kernel has
> > supported UDF for several years, which is as long as it has supported DVDs.
>
> I believe in what you say, but actually I can mount a video DVD both as
> UDF and ISO9660. As you say, Nautilus and "mount" unlock the DVD before
> mount it, that's why I always can mount it.
>
> Yet, I don't understand why dd should not copy a stream of byte from a
> device if they represent an encrypted video DVD. I mean, whatever the
> bytes represents, dd should dump them. At most, you should get a big,
> useless file, but that file should be exactly what was written on the media.
>
> But probably there's something I don't know. You said that mplayer (and
> obviously xine, vlc and so on) unlocks the drive, and I guess you mean
> "at the hardware level". If it's so, every tools like dd, tar, cpio and
> such should fail reading the media.
>
> Am I right?
>

If I understand correctly, tar and cpio are file archiving tools.
dd does a byte-for-byte transfer, so it should capture everything
on the DVD, including encryption.

> Another question: is there something one can do before invoking dd to
> accomplish the same without using mplayer? I have nothing against
> mplayer, it's just curiousity.
>
>

I don't know, is there any way to mount it as a udf file system???

Kind regards,
Nancy
 

--
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http://www.ncsa.uiuc.edu/~nrudins/

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

Phillip Susi
In reply to this post by Andrea Giuliano
Andrea Giuliano wrote:
> I believe in what you say, but actually I can mount a video DVD both as
> UDF and ISO9660. As you say, Nautilus and "mount" unlock the DVD before
> mount it, that's why I always can mount it.
>

What do you mean you can mount it as iso9660?  If the disk is UDF you
certainly can't mount it as iso9660.  Usually your /etc/fstab will
specify udf,iso9660, which means EITHER filesystem is acceptable, and
both will be tried until the correct one is found.

> Yet, I don't understand why dd should not copy a stream of byte from a
> device if they represent an encrypted video DVD. I mean, whatever the
> bytes represents, dd should dump them. At most, you should get a big,
> useless file, but that file should be exactly what was written on the
> media.
>

Because the encryption is done at the hardware level, the drive will
refuse to read those sectors unless it can correctly decrypt them.  The
firmware in the drive will return an error rather than the encrypted data.

> But probably there's something I don't know. You said that mplayer (and
> obviously xine, vlc and so on) unlocks the drive, and I guess you mean
> "at the hardware level". If it's so, every tools like dd, tar, cpio and
> such should fail reading the media.
>
> Am I right?
>


Yes, all those tools will fail if the drive has not been unlocked, and
will work if it has.


> Another question: is there something one can do before invoking dd to
> accomplish the same without using mplayer? I have nothing against
> mplayer, it's just curiousity.
>

I'm sure there is some other way to unlock the disk, but I don't know of
one.  It's easy enough though to just fire up mplayer for a second ;)



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

Phillip Susi
In reply to this post by Arne Caspari-2
No, the encryption is done at the hardware level.  The drive will fail
to read the encrypted sectors if it can not decrypt them.

Arne Caspari wrote:

> Phillip Susi wrote:
>> It unlocked the disk, which means it sent the drive a valid key to
>> decrypt the encrypted blocks.
>
> Correct me if I am wrong but AFAIK not the disc is encrypted but only
> the video .VOB files.
>
> So in my optinion, dd should work :-/
>
>
>  /Arne
>


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

Andrea Giuliano
In reply to this post by Phillip Susi
Phillip Susi wrote:

> Andrea Giuliano wrote:
>
>> I believe in what you say, but actually I can mount a video DVD both
>> as UDF and ISO9660. As you say, Nautilus and "mount" unlock the DVD
>> before mount it, that's why I always can mount it.
>>
>
> What do you mean you can mount it as iso9660?  If the disk is UDF you
> certainly can't mount it as iso9660.  Usually your /etc/fstab will
> specify udf,iso9660, which means EITHER filesystem is acceptable, and
> both will be tried until the correct one is found.

I mounted "Shrek" right now, without any options, and it was mounted as
ISO9660. I umounted and remounted it as UDF ("-t udf"), and now it is
mounted as UDF. Here are "ll /mnt" in both cases, first ISO9660, then UDF:

total 745
dr-xr-xr-x  1 root root   2048 2001-09-14 01:34 audio_ts/
-r-xr-xr-x  1 root root     73 2001-09-06 14:28 autorun.inf*
dr-xr-xr-x  1 root root   2048 2001-09-06 14:27 common/
-r-xr-xr-x  1 root root    173 2001-09-06 14:28 disc.id*
-r-xr-xr-x  1 root root 734208 2001-09-06 14:28 install.exe*
dr-xr-xr-x  1 root root   2048 2001-09-06 14:27 mepatch/
-r-xr-xr-x  1 root root  14914 2001-09-06 14:28 readme.txt*
dr-xr-xr-x  1 root root   4096 2001-09-14 02:56 video_ts/
dr-xr-xr-x  1 root root   2048 2001-09-06 14:28 win/

total 750
dr-xr-xr-x  2 4294967295 4294967295     40 2001-09-14 01:34 AUDIO_TS/
-r--r--r--  1 4294967295 4294967295     73 2001-09-06 14:28 AUTORUN.INF
dr-xr-xr-x  4 4294967295 4294967295    232 2001-09-06 14:27 common/
-r--r--r--  1 4294967295 4294967295    173 2001-09-06 14:28 disc.id
-r--r--r--  1 4294967295 4294967295 734208 2001-09-06 14:28 install.exe
dr-xr-xr-x  4 4294967295 4294967295    236 2001-09-06 14:27 MEPatch/
-r--r--r--  1 4294967295 4294967295  14914 2001-09-06 14:28 README.TXT
dr-xr-xr-x  2 4294967295 4294967295   2068 2001-09-14 02:56 VIDEO_TS/

Please note that I can't say how this happened, just show you what I did
and the result. I had the same result with all other video DVDs I tried.
  Most of them just have the canonical dirs "audio_ts" and "video_ts".

>
>> Yet, I don't understand why dd should not copy a stream of byte from a
>> device if they represent an encrypted video DVD. I mean, whatever the
>> bytes represents, dd should dump them. At most, you should get a big,
>> useless file, but that file should be exactly what was written on the
>> media.
>>
>
> Because the encryption is done at the hardware level, the drive will
> refuse to read those sectors unless it can correctly decrypt them.  The
> firmware in the drive will return an error rather than the encrypted data.

Clearly, dd is to simple to unlock the drive, but see below...

>
> I'm sure there is some other way to unlock the disk, but I don't know of
> one.  It's easy enough though to just fire up mplayer for a second ;)
>
I agree!

Best regards.
>
>

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Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302

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

Andrea Giuliano
In reply to this post by Phillip Susi
Phillip Susi wrote:

> Noah Dain wrote:
>
>> As far as encryption on dvds go, the dvd itself isn't encrypted, just
>> the .vob files on it.  So, if you can't see the VIDEO_TS directory
>> with .vob (mpeg) files in it, then the problem is not with normal dvd
>> encryption.
>>
>
> Actually, the DVD itelf _is_ encrypted, just not the whole thing.  The
> sectors that contain the vob files are encrypted at the hardware level,
> which is why dd can not read them.  The drive itself performs the
> decryption of those sectors once it has been unlocked.  If the data file
> itself were encrypted, then you would still be able to read and copy the
> file even though you could not understand it's contents.
>
I must agree with Noah: just VOB files are encrypted, and not at the
hardware level. That doesn't explain the strange dd's behaviour, but
explains what mplayer does, described in the following two points:

1. First case: no libdvdcss2. Remove libdvdcss from your system, put
your favourite movie into the drive, and run "mplayer dvd://" in a
terminal. Personally, I get this output (shortened):

MPlayer dev-CVS--4.0.2 (C) 2000-2005 MPlayer Team
CPU: Intel Pentium 4/Xeon/Celeron Northwood (Family: 8, Stepping: 4)
Detected cache-line size is 64 bytes
CPUflags:  MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled for Debian.

.....

Playing dvd://.
libdvdread: Encrypted DVD support unavailable.
************************************************
**                                            **
**  No css library available. See             **
**  /usr/share/doc/libdvdread3/README.Debian  **
**  for more information.                     **
**                                            **
************************************************
Reading disc structure, please wait...
There are 13 titles on this DVD.
There are 21 chapters in this DVD title.
There are 2 angles in this DVD title.
DVD successfully opened.
Cache fill:  0.00% (0 bytes)    Encrypted VOB file! Read
DOCS/HTML/en/dvd.html.
Encrypted VOB file! Read DOCS/HTML/en/dvd.html.
Encrypted VOB file! Read DOCS/HTML/en/dvd.html.
Encrypted VOB file! Read DOCS/HTML/en/dvd.html.
Encrypted VOB file! Read DOCS/HTML/en/dvd.html.
Encrypted VOB file! Read DOCS/HTML/en/dvd.html.

.....

The result is that you cannot watch the movie.

2. Second case: libdvdcss2 is on. Same steps as above, but here is the
output from mplayer:

MPlayer dev-CVS--4.0.2 (C) 2000-2005 MPlayer Team
CPU: Intel Pentium 4/Xeon/Celeron Northwood (Family: 8, Stepping: 4)
Detected cache-line size is 64 bytes
CPUflags:  MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled for Debian.

.....

Playing dvd://.
libdvdread: Using libdvdcss version 1.2.5 for DVD access
Reading disc structure, please wait...
There are 13 titles on this DVD.
There are 21 chapters in this DVD title.
There are 2 angles in this DVD title.

libdvdread: Attempting to retrieve all CSS keys
libdvdread: This can take a _long_ time, please be patient

libdvdread: Get key for /VIDEO_TS/VIDEO_TS.VOB at 0x000002b7
libdvdread: Elapsed time 1
libdvdread: Get key for /VIDEO_TS/VTS_01_0.VOB at 0x0005271b
libdvdread: Elapsed time 0
libdvdread: Get key for /VIDEO_TS/VTS_01_1.VOB at 0x000954fe
libdvdread: Elapsed time 0

And there comes the movie!

This, to me, means that the disk is not encrypted, so that you can mount
it, "cat" it, "dd" it and so on. But if you want to watch the movie, you
need to decrypt every single VOB file. Nothing makes me think of a
hardware level encryption.

I'd really appreciate your interpretation: I definitely am not a
technician, as you instead maybe are.

Best regards.

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Andrea Giuliano, Ph. D.
ICCU - Istituto Centrale per il Catalogo Unico
Viale Castro Pretorio 105, Rome - ITALY
Tel. +39 06 49210403, Fax +39 06 4959302

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

Phillip Susi
Andrea Giuliano wrote:
> I must agree with Noah: just VOB files are encrypted, and not at the
> hardware level. That doesn't explain the strange dd's behaviour, but
> explains what mplayer does, described in the following two points:
>

Only the parts of the disc that contain the vob files are encrypted, but
it is most definitely done at the hardware level.  The player itself
must decrypt those sectors and it can not ( because it has not been
unlocked ) it fails requests to read them.  This is why dd can not read
the disc.

<snip>

>
> This, to me, means that the disk is not encrypted, so that you can mount
> it, "cat" it, "dd" it and so on. But if you want to watch the movie, you
> need to decrypt every single VOB file. Nothing makes me think of a
> hardware level encryption.
>

Again, only the sectors that contain the vob file are encrypted, which
is why you can mount the disc and see the filesystem directory
structure.  This is also why dd manages to read the first couple of
sectors, then fails when it hits the ones containing the vob files.

If only the file data itself were encrypted, then you would easily be
able to copy the disc, and that's exactly what the MPAA wants to prevent
you from doing.

> I'd really appreciate your interpretation: I definitely am not a
> technician, as you instead maybe are.
>
> Best regards.
>


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