[mythtv-users] SDI with embedded audio and MythTV (suggestions?)

[Andre Newman]

On 19 Feb 2009, at 14:57, Matt Christy wrote:

> Good Morning All,
>
> 	We're an independent non-profit television station serving the  
> greater Philadelphia market. Recently we acquired additional  
> satellites to receive feeds, and we are interested in recording the  
> feeds to MPEG-2 for broadcast at a later time. Our satellite  
> receivers are Sencores that output an SDI signal with embedded  
> audio. I've been having difficulty finding recording cards that are  
> compatible with MythTV that support digital SDI with embedded audio.
>

I'm a independent technical consultant working in TV (Networks4TV  
limited) and I use a lot of Linux tools for my broadcast customers,  
I'm  also starting to use MythTV for some Digital Cinema projects.

I use Dektec cards to record satellite transmissions for archive and  
replay (replay usually for time shifting or test purposes though), I  
would suggest that recording the SDI is a really bad place to start,  
it requires a lot of storage and expensive hardware. Also if you are  
recording a satellite transmission it is already compressed, you may  
as well just record the satellite transmission directly and forget  
about SDI until you need to replay. Recording decoded SDI is actually  
going to reduce final quality over recording the transport stream  
directly unless you record uncompressed or very near.

I've used MythTV to record contribution feeds from satellite, it's  
very happy recording 35Mb/s MPEG2 transmissions, no harder for it than  
recording a few low bandwidth channels on the same multiplex, easier  
in fact. Scheduling has to be manual but it's easy enough. Tuning a  
temporary feed is messy but possible, sadly it's not possible from  
MythWeb.

Any of the usual DVBS & DVBS2 cards will work fine when driven from  
the IF out of a broadcast satellite distribution system, provided LNB  
signalling and power is disabled. I've used it on OBs as well at at a  
customers Earth Station in Germany, no real difficulty.

Alternatively Dektec do some great ASI cards (PCI, PCI express or  
USB2) these can record the MPEG2 transport stream and your existing  
Macs can play these back no problem, I have a Mac Pro doing much the  
same at one customer. For the cost of one Dektec card you could buy  
five or more complete MythTV systems that would do the same job.


> 	I searched the archives a bit, and I found some suggestions of AJA  
> cards. Currently we use AJA Kona LSe cards in some of our Macs to  
> capture video off of beta decks. I also know that these cards  
> support SDI with embedded audio. Does anyone know if they work with  
> MythTV? If not, does anyone have any other suggestions? We've looked  
> into pre-manufactured solutions from other vendors, but they tend to  
> be in the 21k-50k price range.
>
> 	Also, I've been doing some reading on the MythTV FAQs that are  
> around, and there have been suggestions that any one MythTV box  
> shouldn't exceed four recording devices. Is this true when recording  
> Digital signals as well? We have four new satellites, which can  
> output a max of 8 feeds at once. I was thinking of building two  
> separate myth boxes with four cards each.

With the right disks and well supported disk controllers you will be  
fine, I'd suggest three systems with overlap, four if recording must  
be guaranteed.

I have one customer recording 12 in car camera MPEG2 feeds (mixture of  
SD & HD) on two 1U PCs, 4 sata disks in each.

I'm assuming you don't have the budget for a Boss recorder or  
Pixelmetrix DVStor or you wouldn't be on this mailing list?

Happy to discuss doing this for you, it's my business.

Andre