[mythtv] HD (HDMI & Analog) capture - was Re: Solution to CableCARD problem?

Andrew Kimpton awk at awkward.org
Tue Jul 10 14:15:03 UTC 2007

Quoting Simon Kenyon <simon at koala.ie>:

> Chris Ribe wrote:
>> We've been reading that for long enough that a few of those years have
>> passed.  There is already one company selling a sub $1000 analog
>> capture card ( http://www.blackmagic-design.com/products/hd/).   If
>> they can offer it to video production professionals for under $1000,
>> that probably means sub $500 consumer models are theoretically
>> possible right now.
> better still, have a look at
> http://www.blackmagic-design.com/products/intensity/
> which is an HDMI-in capture card for either US$249 or US$349, depending
> on whether you want analogue capture as well!

HDMI Capture has two significant challenges (aside from any sort of  
driver/support issue) :

a) The HDMI license agreements require that if you're capture card is  
going to support capturing 'flagged' (ie copy protected) streams you  
must maintain the DRM protection from 'end to end'. This is difficult  
if not fundamentally impossible in an opensource environment (see the  
original posts about CableCard 8-). It's not clear right now how many  
of the STB's out there with HDMI output actually turn on the  
copy-protection features of HDMI, but I can only imagine it's going to  

b) The data rates involved in capture HD images in their uncompressed  
form are large, it takes a significant quantity of storage bandwidth  
to do this type of capture (HDMI is an uncompressed image stream). It  
also of course takes a significant amount of storage (though that is  
less of an issue, but large amounts of fast storage are still  
expensive). Attempting to reduce the data rate (and hence size) by  
compression requires a very capable machine, certainly 2 x dual core  
CPUs quite possibly 2 x quad core CPUs in order to do any sort of  
reasonable compression in realtime. MPEG algorithms are largely  
asynchronous in their compression vs. decompression CPU loads.

Analog capture doesn't suffer from problem (a) however it's expensive  
because it requires some pretty high speed and high quality  
Analog-Digital Converters in order to do the basic frame acquisition.  
It still suffers from problem (b).

I don't mean to sound like a damp squib but the 'acquire HD through  
the analog hole' approach has some significant challenges before it  
becomes something that a larger number of people will be able to afford.

Andrew 8-)

More information about the mythtv-dev mailing list