[DVDnav-discuss] Error in libdvdnav when reading iso images

[Fabian Keil]

Oncaphillis wrote in
http://lists.mplayerhq.hu/pipermail/dvdnav-discuss/2012-May/001722.html:

> I used to create DVD iso images via k3b and played them via VLC.
> With isos of relatively newly released DVD this stops to work and
> VLC fails with the message
> 
>   libdvdnav: demux error! 00 00 00 (should be 0x000001)
> 
> Playing directly from /dev/dvd still works
> 
> The distro is Fedora16
> + k3b == 2.0.2
> + libdvdcss == 1.2.11 ( I also tested 1.2.12)
> + vlc = 1.1.13
> + libdvdnav  4.1.4. I also tried the current SVN build
> 
> I get the same error when playing with mplayer and
> I also tried brasero for iso creation.
> 
> Since direct play works it seems like brasero/k3b have
> problems to create a proper iso and the problems sits
> somewhere in the libs.

The above message can be generated when the ripping program has
generously padded regions with unreadable sectors with binary
zeros and one of the padded blocks is actually referenced in the
ifos.

In this case it's not the result of a bug in the libs (assuming
you meant libdvdnav or libdvdread) but the result of a limitation
in the program that is using them in combination with companies
that interpret the relevant standards somewhat liberal.

I'm not familiar with k3b or brasero and thus don't know if this
is the cause of the issue, but at least it would explain why the
real disc works and the copy doesn't.

I've never seen the issue with discs that haven't obviously
been mastered incorrectly, but I suppose it can also happen if
the disc is scratched.

In my experience, copies of intentionally incorrectly mastered
discs that cause this issue when padding with zeroes, can usually
be played correctly with VLC when padding with other blocks from
the region that have been read correctly instead.

It's not perfect, but can be sufficient to solve the issue.
I'm still experimenting with this, though.

With some of those copies I can trigger at least four different
crashes in libdvdnav 4.2.0's dvdnav_describe_title_chapters(),
that aren't triggered when ripping with zero padding which lets
VLC rejects the disc right away.

Recent VLC versions use this function, but one can work around
it by undefining HAVE_DVDNAV_DESCRIBE_TITLE_CHAPTERS. VLC 1.1.3
doesn't seem to use the function yet and thus correctly plays the
copies out of the box (I only confirmed the latter).

One of these issues has already been fixed after the libdvdnav 4.2.0
release (https://bugs.launchpad.net/ubuntu/+source/libdvdnav/+bug/934471)
but as far as I can tell the others still exist, or at least don't seem
to be fixed in https://github.com/microe/libdvdnav and I haven't seen them
mentioned when crawling the archives either.

I attached the patches that seem to prevent these crashes for me.
I'd appreciate comments on whether or not the skip conditions
are reasonable, especially the one in patch 3.

Note that I ran into the issues with copies where I now know that the
padding has been done somewhat sloppy. I haven't tested yet if these
crashes can be reached by playing the original discs. If not, I suspect
that with a fancier padding algorithms the copies might play correctly as
well.

Fabian
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