> Even DTS discs will likely include Dolby
> Digital (though it might not be 5.1) because there isn't enough space
> to do PCM and DTS while keeping the video quality high.

DTS is doing the same thing they did on laserdiscs -- completely
replacing the PCM soundtrack with their own format.  They will
probably not include Dolby Digital at all, because that's a
competitor.

> I'm not sure about DVD-ROM-- presumably the ones currently available
> use PCM just like their CD-ROM counterparts.

~All current discs including a stereo PCM soundtrack, and most of them
include surround sound in Dolby Digital format.

> Ick.  It sounds like the best way to get DD would have to be hardware,
> then.

The AC-3 spec is actually publically available (as part of the
ATSC/HDTV effort), and writing a decoder isn't that hard.

The real problem for DVD is the Content Scrambling System, which
negotiates a session key and encrypts the data as it travels between
the reader and the decoder board.  This can almost certainly be
reverse-engineered from a software-only decoder, but AFAIK nobody's
published the results yet.