[mythtv-users] Beginner Question

Joseph Caputo jcaputo1 at comcast.net
Sun Dec 19 14:20:49 UTC 2004

Gerald S wrote:
> Hello All,
> I am doing all my research before I dive into my MythTV HD project (I am new
> to Myth & Linux, and fairly new ot HD...so bare with me:).  I am using a
> digital cable box from Time Warner.
> I understand that my cable stream is encrypted going into my cable box,
> which requires me to use their box.  But why can't cards like pcHDTV3000
> read the component video coming out of my cable box.  I know it whould need
> to handle QAM for HD, but once that is done there is still the issue of
> being encrypted by the cable company.  How can that be encrypted, my TV
> would have to know how to unencrypt it?  Why can't I let the box do the
> unencrypting and just take the signal before it hits the TV?
> Is this because it is HD?  Or digital?  Wouldn't this work on just normal
> analog cable, that did not need a cable box?

If you have digital cable, your digital channels come in over your cable 
as MPEG-2 in a QAM transport.  A pcHDTV3000 is supposed to be able to 
tune/decode these channels once the upgraded driver/firmware is 
released.  However, as you're aware, most of the channels are likely to 
be encrypted by your cable provider, thus negating (most of) the 
advantage of having that card.

The component video coming out of your cable box is raw video, not MPEG 
data.  Your cable box has already done the work of decrypting and 
decoding the signal.  Thus, it's now an analog signal and you need a 
regular capture card (bttv card, PVR-x50, etc) to capture it.  Think 
about it... you suggest "taking the signal before it hits the TV", but 
your TV can't decode MPEG, so it's got to be raw video, neh?

What you want to do *may* be possible, as the FCC has required cable 
operators to provide an enabled FireWire port that you may use to 
capture the digital (MPEG) data that your cable box has decrypted (but 
not decoded).  The catch is the content accessed via FireWire will not 
be HD... any HD content will have been transcoded down to a lower 
resolution (say, 480p).  In any event, Myth does not currently support 
capturing video over FireWire.



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