[mythtv-users] HD capture via Component/RGB/DVI incoming at 720i

Michael T. Dean mtdean at thirdcontact.com
Fri Jul 1 21:20:39 UTC 2005

Todd Bailey wrote:

> It there anyway to perform an  video + audio mixed in capture on the 
> above listed hd signals and resolution?

Not for under $1000.  Maybe for under $10,000.  Probably for under 
$100,000.  At the prices involved and because the solutions available 
are all for "specialized" uses, no one posts prices on the web, but feel 
free to call a few vendors to see for yourself...

Just decoding a High-Def MPEG-2 stream takes significant processing 
power.  Encoding it real-time takes extremely expensive dedicated 
processing devices

(Note, although some of these are listed as DVB, the US's ATSC format is 
basically DVB with some modifications to give the "not invented here 
crowd" a nice warm feeling, so many broadcasters are converting DVB 
equipment for use with ATSC.)

or, to build your own,


> I am on satellite and those are the only hdtv signals available to me, 
> cable or off the air is not an option.
> I believe there is a something called sdi that is either a interface 
> or a signal standard that professionals use for hd video.
> perhaps it's something similar to firewire?

SDI is the Serial Digital Interface and is the basis of digital transfer 
mechanisms such as DVI (Digital Video Interface) and HDMI 
(High-Definition Multimedia Interface) as well as other audio and video 
distribution formats.  If you can get this from your receiver (and into 
the computer), you'd be able to use option a) below...

> another item to consider is hacking into the sat receiver and getting 
> the signal after it's been decrypted and building a interface that way.
> I am using one of echostar's dishnetwork receivers (a model 811).

Make sure you read your usage agreement from DISH...

> I'd be open to a solution under $1000 to capture hd and time shift for 
> later viewing.
> I am somewhat new to hd so any suggestions, comments, concerns or 
> advice welcome.

If you want the sub-$1000 HDTV encoder, you have two options:  a) tons 
of hard drives, some as-yet-unavailable signal aquisition device, and 
nowhere-near-real-time encoding or b) wait a few years for the prices to 
drop (assuming that special interests--i.e. MPAA--don't prevent this 
from happening).

For a), you'll need some way to get the digital image into the computer 
and a lot of hard drive space.  The BTTV frame grabber cards work with 
NTSC-sized images, so it would require some way of splitting the signal 
and "tiling" the picture among them then "stitching" it back together.  
For DVI or HDMI, I don't know of anything that will dump the digital 
image (with or without conversion to RGB), but there may be devices that 
can do it.

As for the hard drive space, uncompressed 16-bit color video in 720x480 
interlaced (NTSC) takes about 70GiB/hr (or 105GiB/hr in 24-bit color).  
For ATSC, storage requirements are significantly higher.  You mention 
720i format, but that's not a valid format according to ATSC ( 
http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html ), so I'll assume you 
mean 720p.  A single frame of 720p video takes 1.75MiB at 16-bit color or 
2.6MiB at 24-bit color.  Below are the hourly storage requirements.

Format      16-bit Color    24-bit Color
------      ------------    ------------
720p24      148 GiB/hr      222Gi B/hr
720p30      185 GiB/hr      278Gi B/hr
720p60      371 GiB/hr      556Gi B/hr=1.33Gb/sec

Note that if you have any 1080i channels, storage requirements will 
increase (uncompressed 1080i60 in 24-bit color requires 626GiB/hr)--and 
none of these numbers include audio.  So, although it's possible, you 
won't get much TV for under $1000.  Especially once you factor in 
encoding time--likely to be (much) greater than 6hrs to encode 1hr of video.

Currently, the only really workable solution is OTA capture cards 
and--for the lucky ones whose cable companies don't encrypt their 
high-def channels--QAM capture cards or firewire capture (with capable 
receivers).  Sorry to be the bearer of bad news.


BTW, next time you send a message to the list, I suggest you click the 
"New Message" button and copy the address into the "To:" field or right 
click the address and select "Compose Mail To" instead of replying to an 
existing message.  Your message was buried beneath a thread that I 
didn't care about, so it almost got deleted with the rest...

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