Re: [PLUG] Sorta OT, working with VCD and DVD players

[gabriel rosenkoetter <gr@eclipsed.net>]

On Thu, Jan 24, 2002 at 08:26:16AM -0500, Anthony Locascio wrote:
> Lets see, I like to download stuff from the net.  Some of this stuff is 
> movies that come in the form of a .avi or a .mpeg or whatever.  I can 
> then put some of them to disc (others are simply too large) and others I 
> can watch directly on my computer.  (I have a 36 inch HDTV hooked up to 
> my computer)  But but but BUT, when I burn a said image to a disc, and 
> then proceed to run downstairs and try it in a standalone DVD player, 
> the player will not read the said disc.

There are a few misconceptions here.

First, .avi, as a suffix, says precious little about the actual file
format, even presuming it's anything that's properly a version of
AVI, which I've found NOT to be a safe assumption downloading things
from the Internet... not just because of Windows viruses, but more
because people think "avi" and "mp[e]g" mean "movie". (They don't.
They refer to specific standards.)

Part of what actually matters is what file(1) says about these
files. AVIs will be something like:

foo: RIFF (little-endian) data, AVI

MPEGs will look like:

bar: MPEG system stream data

But even that doesn't tell you all you need to know, as AVIs can be
(validly) encoded in a variety of ways. (The popular one you're
probably seeing is some version DivX. I think there are several
versions of that, though.) MPEGs also come in a variety of versions
and layers. (MPEG-1 only has one layer, MPEG-2 has video and audio
layers, newer MPEG versions have to do with better video codecs.)

Note that the format commonly referred to as mp3 is actually MPEG-2,
layer 3 (which is audio only). Your system's magic (somewhere around
/usr/share/misc, probably) likely has a special entry for mp3s that
will make file(1) say something like:

qux: MP3, 128 kBits, 44.1 kHz, JStereo

Second, DVD != VCD != <foo>, where <foo> is some file you
downloaded. Those on-disc formats are specific and consumer players
for them won't play anything that isn't the right format. (The
on-disk--note the k--formats are also specific, but software exists
to read all of them. That's not the case with the stuff in most
consumer players, since it's all burned to a ROM of some sort and
updating it is considerably more of a hassle than recompiling or
installing a new version of the software on a computer.)

DVD needs to be mpeg2 video "encrypted"[1] in a special way with (I
*think*, but don't quote me on it) the audio track separate (this is
how DVDs can let you switch between a variety of audio tracks for
various languages and directors' commentary without separate video
tracks, which would force a huge reseek of the disc every time you
switched audio on the fly, which doesn't happen). You may recall
reading about this format wrt DeCSS.

VCD needs to be (again, I'm not sure, don't quote me on it) mpeg2
(3?) video+audio. Writing that out in the right way (I don't know
what the right way is, but it's almost definitely not to embed the
mpeg within an ISO-9660 file system on-disc) to a CD should mean
that a consumer DVD player that can also play VCDs can play your
CD. Some tinkering will be necessary, but CD-Rs are quite cheap
(and you'd probably only need to use one CD-RW).

[1] In quotes because it's not, properly, encryption. The standard
includes master keying, which means there's always a back door,
which means your data isn't actually encrypted at all to a
moderately resourceful attacker. Again, cf DeCSS.

-- 
gabriel rosenkoetter
gr@eclipsed.net

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