Re: [gentoo-user] DVD Movie backups

[Michael Mol]

On Fri, Dec 16, 2011 at 12:25 PM, Mark Knecht <markknecht@×××××.com> wrote:
> On Fri, Dec 16, 2011 at 9:06 AM, Michael Mol <mikemol@×××××.com> wrote:
>> No; you'll have to decrypt, or do without the encrypted bits.
>>
>> dvdbackup is probably the closest to what you want.
>>
>> On Dec 16, 2011 11:09 AM, "Mark Knecht" <markknecht@×××××.com> wrote:
>>>
>>> For archive purposes is there a simple way for me to make a
>>> bit-for-bit copy retail DVDs I've purchased?
>>>
>>> Assume that I've got the right sort of DVD drive, I guess something
>>> capable of writing dual-layer DVDs.
>>>
>>> Thanks,
>>> Mark
>
> Interesting. So even something that just copies blocks of data, like
> dd, can't be used for that purpose?
>
> I have no interest in tearing apart the DVD in any way. It was more
> about the idea of a fire causing the loss of maybe $15K-$20K
> investment over the years. I can rip all the CDs, keep the ripped
> version here to watch on the computer, and store the DVDs elsewhere,
> but that elimiates (generally) being able to watch special features
> which my wife and kid enjoy.
>
> Thanks for the info.

I did exactly the same thing a few years ago, but it's been a long,
long time, so my memory on my process is very fuzzy. (It also involved
my first foray into RAID...I've got a couple hundred DVDs!) Go ahead,
count the number of times I qualify something with "IIRC"...

dvdbackup can recreate the ISO images, IIRC.

If you run a simple 'dd' on a DVD with encrypted portions, you'll get
I/O errors when it encounters the encrypted pieces. IIRC, some of the
data required to decrypt those portions is on the disc, but it's in an
out-of-the-way portion that won't show up as part of the block device.
IIRC, dvdbackup makes use of libdvdcss to decrypt the encrypted
portions[1], and writes a decrypted version of the data. *this* is why
you can't make a bit-for-bit copy; the output data would be decrypted.

There are other, later obstacles, too; once CSS was broken, some
content publishers (Bandai USA, for example) would fudge the ISO spec
and the DVD nav specs in ways that didn't break *most* hardware DVD
players, but did tend to break players which strictly adhered to the
standards, such as ffmpeg, vlc and mplayer. It also broke dvdbackup
for me, IIRC, which is why I had to resort to vobcopy in some cases. I
expect the software angle for handling these things has gotten better,
though.

[1] I don't know how it does it when dd would have hit an I/O error.
Obviously, my understanding of the workings of dvdbackup, dd, DVDs and
CSS encryption is flawed somehow.

-- 
:wq