[mythtv-users] HDTV, Myth, HD-2000, HD-3000, questions galore (and hopefully answers from the smart people... )

Brad Templeton brad+myth at templetons.com
Tue Jan 18 18:17:30 EST 2005


On Tue, Jan 18, 2005 at 02:23:16PM -0800, Julian wrote:
> Brad,
> 
> This is where my hopes of capturing the stream after
> the set top box started.  Too bad they were dashed. 
> Anyway I have read that the cable companies can detect
> how much bandwidth you are consuming...so viewing the
> content without paying is risky.  Oh well, I guess the
> easy answer to capturing encrypted streams is that it
> can't be done today.

No, in a system as I have described (which is not the only system,
but a common one) they can't detect how much bandwidth you are
consuming.   It's a one way RF stream.  You are getting all of it,
all the time, and just listening.   Their cable box could report
back what you watch but I don't think they do except for PPV, if they
do they had better state it in their privacy policy and get your
agreement!

A VoD system would know what you watched, though.  They are not
common.


Too fill in some numbers I left out, today many cable companies
use 256-QAM, which has 39 megabits per channel.   The channels
take about 6mhz.

An SD signal takes about 3.5 megabits, which implies they can get
about 11 of them into a single channel.   HD signals take more, about
18 megabits (a bit less for 720p) so you can get 2 of them on a 256-QAM
channel, though with lower data rates on the HD, there are people who
squeeze in 3 of them.

This is a around twice what 8vsb ATSC sticks into a 6mhz channel.
Though typically we see an ATSC holding one HD channel and one SD, or
4 or 5 SD channels.

But no, you can't decrypt it.  You could if you could get ahold of
the keys and somebody wrote software.   And the keys are sitting in
the cablecards and digital set top boxes, so I am sure some folks
will eventually extract them.  Though of course the keys exist not
just to be a pain in the ass, they are how they control whether you
get paid channels (like HBO, or the digital extended cable channels etc.)

It would be nice if when you paid for the channels they just came in
the clear, but instead they insist you get their set top box or cablecard.

A lot of people seem to not be liking cablecard.  You get to tune with
the tuner in your TV, but you lose any of the fancy features the cable
companies put into the set top boxes -- on screen display, program guide,
PPV etc.





More information about the mythtv-users mailing list