[mythtv] Solution to CableCARD problem?

Rudy Zijlstra mythtv at grumpydevil.homelinux.org
Sun Jul 8 19:15:41 UTC 2007

Tim Moore wrote:
> I’m new to MythTV, so please excuse me if this has already been 
> addressed. I understand the problem with CableLabs certification, and 
> how it will be impossible for an open source solution to obtain it. 
> However, I’ve been doing a lot of research into this, and it seems to 
> me that there is a solution that has been overlooked.
> CableLabs won’t certify a MythTV solution because it would be 
> impossible in an open source solution to prevent access to the 
> decrypted video stream. The reason that Vista can obtain it is because 
> of the closed DRM implementation that MS has built into the operating 
> system and into Windows Media Player. There really is no way to get 
> around this CableLabs requirement, so I propose that the solution is a 
> modified architecture for MythTV that will works with it.
> Essentially, the video path and the control path of the system need to 
> be separated. The video path needs to be closed and “secure” (or, that 
> is, meet CableLabs requirements. We all know that nothing is 100% 
> secure.). It is not good enough to use some video adapter with 
> CableCARD slots (such as the ATI card that Dell is using for its 
> premium cable-ready TV), which decrypts the video signal and passes it 
> to the operating system and media player software. This approach, as 
> we have seen, requires CableLabs to trust the operating system, the 
> media center software, and the hardware. For the ATI card to work on 
> the Dell system, the ATI drivers (written by Microsoft, by the way) 
> check for a code in the BIOS to confirm that it is connected to 
> approved hardware. Getting CableLabs certification costs over $100,000 
> per system, so this approach rules out small system builders, even if 
> they are using Vista. For open source solutions, it rules it out 
> altogether.
> However, we are starting to see hardware manufacturers build 
> single-chip DVR solutions. The Broadcom BCM7118 
> <http://www.broadcom.com/products/Cable/Cable-Set-Top-Box-Solutions/BCM7118> 
> is one such device. This board contains not only a CableCARD 
> interface, but also DCAS support which should eventually supersede 
> CableCARD with a downloadable conditional access system (reducing the 
> high upgrade and support costs for cable companies, and/or users, 
> caused by the current hardware-only solution). The BCM7118 interfaces 
> directly to its own hard disk, securely storing encrypted programming. 
> It contains all the critical components of a premium cable-ready DVR; 
> authentication, authorization, decryption, decoding, storage, 
> graphics, sound and control. You can make a stand-alone DVR from this 
> system, with the addition of a case, hard disk, and some basic 
> supporting electronics. As a complete and closed system, 
> theoretically, the BCM7118 should be able to achieve CableLabs 
> certification. However, I haven’t seen it on the CableLabs approved 
> list so I have emailed Broadcom to find out. I’ll let you know what I 
> hear… Hopefully, it’s in the works.

You will never see the BCM7118 on that list. What you will see is a 
product based on it. Same goes for the 7400, which is essentially a HD 
STB (though it still needs a frontend = tuners).

> The BCM7118 supports an API that allows a connected system to control 
> it. So, MythTV could be modified to use this API to control the 
> BCM7118. I’m sure there must be a graphics card out there that can 
> take the output of the BCM7118 and superimpose on it graphics from the 
> PC, thereby adding a capability to add EPG and other graphics from 
> MythTV. Since the decrypted TV signal is not passed to the MythTV 
> software or operating system, there is no risk of it being copied. 
> That is, no more than the output of any other cable box…
> So, the solution is not to make decryption part of a MythTV system, 
> but to make MythTV a control solution for a bare-bones DVR that is 
> installed inside the PC chassis. Of course, MythTV could still work in 
> the traditional mode for unencrypted media. I realize that this means 
> that the entire solution is no longer 100% open source, but then what 
> system is when you take into account the firmware in the supporting 
> hardware? The important thing is that all of the high-level control 
> software remains open source, and that is where the value is added.
> There is still one small snag. Broadcom doesn’t yet make a single-chip 
> system with HD output (although it can downscale HD to SD). I’m sure 
> that can’t be too far away, and I have emailed them to find out.

Be very curious if you get an answer...

> I think that if the development community can get behind this (and if 
> CableLabs will certify single-chip/board DVRs, as I hope) then MythTV 
> can remain a viable alternative to Vista. If not, then it will surely 
> die as new cheaper alternatives to Tivo become available and more 
> Vista systems get certified.

I do not agree with this last assessment. If that were true Myth would 
have died long ago.

Different usage pattern and requirements.



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