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Re: Please advise: 4channel capture device with HW compression for Linux based DVR




Thanks a huge, it is exhausting!
Please see inline.

Jackson Yee wrote:
Yep, been down that road before myself.

The truth of the matter is that slim profile, multiple port cards are
available with Linux drivers, but they are quite expensive ($500 for
the cheapest that I could find, although it is a very nice looking 16
port system).
Oh, this is too pricy.
Are you talking only about cards with H/W encoding or about all low profile multiple port capture cards?
I have a mini-ITX system sitting by my television right now which I
would love to use my new STK-1160 4-port USB adapter (marketed as
EasyCap 4-port DVR USB) with, but unfortunately, we're still working
out NTSC support for it. The guys using PAL and Zoneminder have
apparently gotten it to work pretty well.
It appears like STK-1160 has 25/30 overall fps, so it's not quite the same thing.
I've never used an Atom system, but from what I understand, although
the CPU is quite power efficient, it is also utterly crushed in
performance by the cheapest dual-cores available today. That's why
Nvidia's Ion platform was so attractive to people looking to do 720p
or 1080p on their televisions - the Atom simply did not have the power
to handle HD video. A D1 stream is much easier to work with, but
encoding is also more processor intensive than decoding by an order of
magnitude. You could probably do one D1 stream with MPEG4, but if you
plan on using real-time x264 or more than one stream... I would have
to believe that your system would be quite incapable of keeping up the
framerate.
It was tricky to make ATOM decode HD, I had to employ multicore CoreAVC decoder. Decoding of 720p was consuming about 30% of CPU time (assuming it has 2 HT cores, each of 4 HW threads was busy 30% of time), and 1020p was about 50-70% AFAIR. It can be outperformed by regular P4.
So my system must be definitely unsuitable for real time encoding :(

Believe me, I would love to say that I have a solution for you since
that would mean a solution for me as well, but the reality of the
matter is that we are just not quite there yet on driver support for a
multiple channel USB capture device. If you're just planning on doing
one D1 stream at a time, the WinTV PVR USB2 has hardware encoding and
is supported quite well. I suppose that you could hook up a couple of
these, but whether the system could handle these USB devices is beyond
my experience.
Yes, there are single channel devices with encoding, combining 4 of them together may be less pricy, but it's odd anyway. :)
Please let me know if you have any success with this project.
It looks it's not worth wasting time trying this on Atom.
I may need to consider an upgrade.
I'm considering Intel mini-itx motherboard. http://www.mini-box.com/Intel-DG41MJ-FSB1333-Socket-775-Mini-ITX-Motherboard The price of the upgrade looks comparable with price of HW encoding solution, but it is more beneficial.

So, could you please say more about LP vs regular PCI capturers (W/O H/W encoding)? Are there inexpensive LP solutions?

Regards,
F S
Regards,
Jackson Yee
The Possum Company
540-818-4079
me@xxxxxxxxxxxxx

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