[mythtv] A new angle on High-Def Satellite capture?

luitjens at cs.utah.edu luitjens at cs.utah.edu
Fri Mar 2 18:36:22 UTC 2007


I think there is a legal gray area in what you are proposing.  This 
would be the same ideal process for capturing digital cable. The problem 
with this is you have to break their encryption scheme and gain access 
to their keys.  There are 2 issues with this first the encryption key is 
likely changed every few seconds making it impossible to brute force 
decrypt it in real time and very difficult to do it in any sort of 
realistic time.  Gaining access to their key changing algorithm would 
solve this part.  The second problem is the DCMA prohibits breaking of 
encryption thus making it illegal.  However there are some exceptions to 
the DMCA involving fair use and one could argue that breaking the 
encryption in order to "time-shift" meets the exception per the betamax 
ruling.

My hope is that sometime in the next year or 2 the system is reworked to 
allow capture cards allowing the elimination STBs. But I doubt this will 
happen without a push by the FCC.  Currently with the DMCA the 
broadcasters are gaining a strong hold on what we are allowed to do.  
I'm afraid that mythtv will lose a lot of usefulness in 2009 when the 
cable companies stop broadcasting analog signals. 

DeRose, Chris wrote:
> I'm new to this list, so forgive me if this email is slightly tangential
> to the project.
>
> I love mythtv. Of course, like so many others, I find the content
> industry's lack of High-def capturing support to be slightly
> infuriating. I like my Directv programming, and I especially like my
> Directv high-def offerings. These offerings are not available via OTA,
> not available via firewire, and I want them to record into my myth
> setup. There's of course the SDI and firewire box mods by a handful of
> companies, but those are a really expensive proposition. So how about a
> new angle?
>
> Instead of focusing on capturing decoded content from out of the
> satellite box, I think a better angle might be to write a software
> interface between the ISO7816 card and the Directv DVB-S satellite
> input . Much like the box does itself. 
>
> The decoding process on those boxes seems simple enough. I believe
> there's three conceptual 'streams' involved in decoding a given channel.
>
> There's the audio stream, which comes down unencrypted, and should be
> fairly easy to access.  I assume its MPEG-2 compressed, but I don't
> necessarily think this matters too much. 
>
> The video comes down as a encrypted, MPEG2 (or soon MPEG4) stream.
>
> And the third, I believe, is an additional 'program instruction' stream
> to be handed off to the card. This instruction stream exists both for
> decoding video and implementing various anti-piracy verifications of the
> card and subscriber's validity. I don't think there's much, if any,
> decryption logic to write if you can simply hand the job off to the
> card. I'm not entirely sure how the decryption process works, but I know
> the bandwidth required for the smartcard interface is minimal - they
> operate (well) off a Serial port. So I'm guessing that some processing
> will be required by the box-emulator code in order to fully
> process(decrypt?) the signal as it comes in through the DVB interface.
>
> The benefits to pulling content this way are obvious:
> 	* perfect quality capture - no re-encoding needed
> 	* Low CPU usage (well, maybe not for the high-def?) since no encoding
> is needed
> 	And Most important:
> 	* No HDMI to crack for HD premium channels! *Legally* recorded high-def
> premium channels!
>
> The only thing I'm not so sure about is whether Directv is sending out a
> standard DVB signal. If it is, there's plenty of DVB cards on the
> market, and I'm thinking allthats needed is a user-space decoding
> process which should be relatively trivial in the scheme of things. If
> its not a standard DVB signal, then the plausibility of this angle is
> murky. Does anyone know the answer here?
>
> So, what do you guys think? Any comments are appreciated. I'd like to
> stress that I'm a legitimate, paying subscriber, and this idea would
> only be able to work for other legit subscribers with a valid, active,
> account card. Unfortunately I can't make the time to work on this. But
> I'd like to spread the idea around, so if a talented programmer who has
> the desire to make a big difference to a lot of people like me, (and
> hell, make a stand against DRM) that the idea is available.
>
>   


More information about the mythtv-dev mailing list