[mythtv-users] HDMI Capture

Gene Stapp genestapp at gmail.com
Mon Sep 18 01:52:08 EDT 2006

Graeme Wilford wrote:
> On 12/09/06, Steve Daniels <steve.p.daniels at googlemail.com> wrote:
>> Just seen this in the register:
>> http://www.reghardware.co.uk/2006/09/12/blackmagic_hdmi_editing/
>> http://www.blackmagic-design.com/products/intensity/
>> Reckon something like that could be used in linux as a capture device for
>> myth maybe?
>> Please feel free to ignore if this is a rubbish idea..
> So presumably, it may be possible to capture off-air HD in the UK?
> Say, taking the component output of a SkyHD box, converting it to HDMI
> using something like this:
> http://www.gefen.com/kvm/product.jsp?prod_id=3569 and then throwing it
> at the intensity card... ?
> I'm stuck with SD on NTL and a PVR350 right now but this does sound
> interesting...
> Cheers,
> Wilf.
I emailed the blackmagic development team about the intensity card. It 
looks like on the fly compression is doable with a dual core from what 
they are saying. It's just a driver/codec design thing now. Uncompressed 
HD would require us to raid 0 about four 500GB drives to have enough 
storage and transfer speed for 4 hours of 1080i content.
here is their reply:

The Intensity card has generated quite a lot of interest with the
Linux and Open Source community, something which we did not expect.

1. In the Windows platform, we allow the user to capture and compress
on the fly to a JPEG format while on the Mac, to DV, PhotoJPEG as
well as DVCPRO HD. A fast processor will be necessary and also a
capture friendly codec. Certain codecs don't fare well with on the
fly compression, d.g. HDV.

2. Uncompressed HD video will require more than 100MB/sec of transfer
rate. I've attached a small clipping from our PDF manual with some
typical transfer rates using the Apple or Blackmagic Uncompressed
4:2:2 and 4:4:4 codecs for your reference.

3. The compression on capture (if chosen) is in real time but this is  
done in software, relying on the processing power of the system. We  
don't have any hardware acceleration built in. Uncompressed capture  
actually requires less processing power.

A. I'm not sure of the requirements for post capture compression but  
dual cores and quad core machines should be fine. We use dual cores  
PCs and Macs in our labs as well. I guess post processing is simply  
takes up less time with more powerful hardware.

4. You're correct. We don't have any Linux drivers. However, the  
response from the Linux community has been good and we've notified  
our engineers about it. Hopefully, this is something that can look into.


Kristian Lam
Blackmagic Design

> I am a user sometimes code contribute of a popular open-source  
> Linux based pvr system – Mythtv. The new Intensity HDMI capture  
> card coming out looks like it may be the perfect hardware input for  
> cable boxes/high def content coming through non-encrypted hdmi. I  
> have some questions about the capability of the hardware that I  
> didn’t see listed on the website or spec sheet anywhere.
> 1. What would it take to compress the video coming in real-time to  
> make the huge amounts of data easier to manage.
> 2. What kind of storage requirements/read and write speed  
> requirements are we talking here. As you know, uncompressed HD  
> takes up massive amounts of space. Many mythtv users run very large  
> raid 5 arrays above 1TB with transfer rates usually between 60MB  
> and 100MB a second (if not higher)
> 3. Does this device use any form of hardware compression or is  
> everything software based.
> A. If it’s hardware or software, what kind of processing power are  
> we needing for compression/partial compression with multi-pass  
> compression later say after the recording is finished. Dual-core?  
> Quad-core? A lot of us run dual processors in the 4ghz range with  
> large amounts of ram.
> 4. I know you currently do not have Linux drivers, but the Linux  
> development community can make those easy enough if the intensity  
> card can be adapted as a HD capture device.
>Gene Stapp

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