[tlug] Re: MPEG stream analyser?

[Tobias Diedrich <ranma@example.com>]

Josh Glover wrote:

> In any case, I know how to do DVD backup. The question that I have
> asked in this thread is simply whether a tool exists to analyse an
> MPEG file and show me data on the individual streams.

I have used "bitrate viewer" a few times (works in wine), but I don't
think that is what you want. :-)

> > (DVDs contain some sort of
> > bytecode interleaved with the video, which is used for menus among
> > other interactive DVD-Features.[)]
> 
> I do not think that is how it works. Menus are accomplished with
> sub-picture streams (that is the same way that subtitles are
> implemented), and the navigation is written into the table of
> contents, AFAIK.

It's a bit simplified, but it works that way.  Of course the menu
overlays (Highlighting the currently selected area) _are_ done with
sub-picture streams, but those are just pictures, you still need the
code that sets registers to select differnt audio/video streams and
switches the subpictures when you move around in your menu.

The dvdauthor manpage states a few facts:

|The  DVD virtual machine processes 16 bit values.  It supports up to
|16 general purpose registers; however dvdauthor reserves  3  for
|internal use.   Thus register 0-12 are avaialable for use and are
|referred to as g0 through g12.
|
|There are also 24 system registers, which can  be  referred  to  as
|s0 through  s23.   Not  all  of these  can be  set.   Many of these
|have pseodonyms.

The manpage mentions only a few system registers, but according to
http://www.dvd-replica.com/DVD/sprm.php the region code is stored
in s20.

The code executed in this virtual machine can set user prohibitions
(Disable menu keys and such), check parental settings, jump to
different chapters and titles of the disc or stop playback, switch
subpictures streams, angles and audio.  Basically it has full
control over the player (Unless you use mplayer, which does not
implement the VM, but also can't show you the DVD menus because of
this).

> > Since one of the player registers contains the region code it is possible to check 
> > against it and refuse to play if it doesn't match).
> 
> This is possible, except that I have never seen a player that is not a
> game console that will not play unencrypted DVDs (the PS2 refuses as
> an anti-piracy measure), since it is completely legitimate for a movie
> studio to produce one such disc. Every once in awhile, I find a
> Hollywood movie in my collection that is not encrypted. Many
> non-Hollywood discs are not encrypted, notably in my collection:
> "Revolution OS". [1]

I have a few unencrypted video discs too.  But I rather meant discs,
that check for the region code (which is completely unrelated
to the CSS-Encryption) in their virtual machine code and could then
refuse to play.  Normally the region code is checked by the player
itself and not again by the disc.

> > But at least for Backups this
> > should be a viable way, as long as the DVD-Content fits onto one
> > DVD, but with the advent of dual-layer DVD-R this shouldn't be a big
> > problem any longer.
> 
> Can you afford dual-layer media? I sure cannot. Compare roughly US$
> 0.40 for a single-layer, DVD+ or -R disc to US$ 8.00 or so for a
> dual-layer DVD!

I have to admit, even though I own a dual-layer burner, I never felt
the need to buy dual-layer DVD-R so far, so I don't know the current
pricing for those.  But I would expect the price to fall. :-)

> > I guess we might not get as lucky with the next-generation video
> > format (HD-DVD?).  OTOH, since the vast majority of people won't care
> > about being locked into their region, maybe they won't make it too
> > difficult for the modders.
> 
> I do not see how any technical advance is going to change things much.
> The greedy media conglomerates come up with some half-assed
> "anti-piracy" (read: anti-consumer) scheme, which DVD-Jon or some
> other enterprising hacker breaks in a month. Like Dr. Turnbull said,
> copy-protection is to stop Joe User, not Bob the Audiophile, who
> *will* find a way to play his music his way.

I certainly hope so, but some recent developments are a bit
worrying, I'm thinking of HDMI/HDCP and I also recently read about a
surround-amplifier, which would refuse to route digital inputs to
analogue outputs for copy-protection reasons (Well, except the speaker
terminals).

But since the signals have to be decrypted at some point, I guess
the whole effort will be futile in the end. :-)

Cheers,

-- 
Tobias						PGP: http://9ac7e0bc.uguu.de