[mythtv-users] External Channel Change Script for DVB cards

Simon Hobson linux at thehobsons.co.uk
Sun Oct 30 12:29:16 UTC 2011

Raymond Wagner wrote:

>  > But if I spit the input to the cable box then let the cable box and the
>>  QAM card tune the same channel.  I am only using the cable box to
>>  request the cable co to send that channel to my house.  Once it is being
>  > broadcast I can receive it normally on the QAM card.

>You would have absolutely no idea where it is sending that channel to,
>so you would have no way to tune it with the QAM tuner.

Bear in mind I have no experience whatsoever with cable ...

Do they encode each channel/mux specially for each subscriber, or do 
they just turn on/off passing of a specific mux to that outlet on the 
distribution unit ?

Just looking at what makes sense from an engineering/business POV, 
it's a lot of electronics (and hence cost and power requirement) to 
individually generate muxes for customers, more so to generate custom 
channel encodings. It would make more sense to just turn on/off 
transmitting a bitstream - which would of course have a fixed 
identifier across the network.

Alternatively, to save having to have multiple RF sections per 
customer, they might generate a mux per customer using just one 
carrier frequency - but I'd still expect the channel identifier to 
stay consistent.

And as someone else has already said - it may be encrypted anyway.
I's suggest the OP tries it. Select a channel on the cable box, and 
see what they get doing a channel scan. Repeat with various 
permutations and see what the cable co is stuffing down the wire - in 
particular whether they are using one or multiple carriers, and 
whether the program identifier stays the same for each channel when 
it's selected.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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