Experimental Physics and
Industrial Control System

[email protected] · Mon, 30 Aug 2010 12:46:27 -0700

John,

I use mpeg4 streaming with axis servers ('blade' video server a243q)
I use linux IOC/OPI with axmjpeg based iocs (for video statistics)
and gstreamer/phonon/mplayer for video display.

As far as the network, well I use a 4G LAG (4* 1G cat6 physical link aggregated = a logical 4Gbps link) as a control network backbone.
For video streams, I use multicast protocols (1 stream of data for video processing and display on several stations)

Now, I remember having a friendly but tense discussion about video feeds on this mailing list.
Some of us prefer running 60Hz, 2Kx2K pixels, not-compressed video on firewire link.
For me 25Hz, mpeg4, black and white, 640x480 over the network works like a charm.
I configure the bandwidth usage based on video required size, refresh rate, pixel depth,  bit rate, whenever required.

With mpeg4, required bandwidth is one of the lowest of all the video standards.
Common video server can stream at 1Gbps (constraint of the network card)
So if you put 12 cameras on 1 network interface (i.e. server), despite variable rate, you will still get a 1Gpbs max output.
When you saturate the network card, you start pixelating.
You need to design # cards/network interface based on the 'expected' changes in the video image.
(our cameras are always pointing in the same direction and the background stay the same)
(so delta in temporal frames is small)
(compression intra frame is also high as 50% of the image is black)

BEWARE:

Transmission lattency can be an issue.
compression + routing/transmission + decompression is ~ 1 sec here.
but it can easily go to the 3 sec range if not careful.
My operators expect 'real-time' video, i.e. to see exactly what is happening RIGHT NOW.
A lag > 1 sec is an issue here.
-> end station processing need to be optimized (profiling, pseudo coloring, etc.)
-> # of switches between display stations and video sources need to be minimized
(3 $200 switches in our case)

Overall:

Our philosophy here is 'everything' over ethernet.
Our move from coaxial to ethernet based video was very successful.

Good luck,

-- 
Emmanuel

On 10:54 Fri 27 Aug     , John Dobbins wrote:
> All,
>
> Of those of you transmitting digital video signals as part of your controls network I am wondering if you are transmitting video on your EPICS subnet or on a separate network. What if any special arrangements have you made do deal with the potentially large throughput from video sources. (Hope the question doesn't seem overly vague, we have varying ideas here about how video should be handled and I am curious about other labs experience - as compared to our inexperience.)
>
> Regards and thanks,
>
> John Dobbins
> Lab for Elementary Particle Physics
> Cornell University

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System