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Recording VGA output ?

 
 
Wim Godden
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      09-21-2005, 11:12 AM
I'm looking for a way to connect a VGA output to a system, so we can
record whatever the user is doing. We would use a split-system to split
between the user's own monitor (actually a beamer) and the recording
system. However, we have no idea how to record a VGA signal. Can we use
3 analog inputs combined to reconstruct the image, then save it as a set
of JPEGs ? Or are there easy conversion systems ?
We would need to make it as small as possible, so PC/104 or similar
formats are advisable.

Any help most appreciated !

Kind regards,

Wim

 
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larwe
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      09-21-2005, 11:39 AM

> I'm looking for a way to connect a VGA output to a system, so we can
> record whatever the user is doing. We would use a split-system to split
> between the user's own monitor (actually a beamer) and the recording
> system. However, we have no idea how to record a VGA signal. Can we use


You can use a VGA-to-NTSC converter and record it on videotape.
However, it's much more efficient to record the operations of the
device that's generating the VGA output, and reconstruct the output by
simulation later.

 
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Wim Godden
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      09-21-2005, 03:35 PM
larwe wrote:

> > I'm looking for a way to connect a VGA output to a system, so we can
> > record whatever the user is doing. We would use a split-system to split
> > between the user's own monitor (actually a beamer) and the recording
> > system. However, we have no idea how to record a VGA signal. Can we use

>
> You can use a VGA-to-NTSC converter and record it on videotape.
> However, it's much more efficient to record the operations of the
> device that's generating the VGA output, and reconstruct the output by
> simulation later.


The idea is to record mutiple systems and store it on a computer system, so
it can be downloaded by others on an intranet. Recording on the device is not
an option, since there's several operating systems involved.

Any suggestions ?

Wim

 
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larwe
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      09-21-2005, 03:42 PM
> > You can use a VGA-to-NTSC converter and record it on videotape.
> > However, it's much more efficient to record the operations of the
> > device that's generating the VGA output, and reconstruct the output by
> > simulation later.

>
> The idea is to record mutiple systems and store it on a computer system, so
> it can be downloaded by others on an intranet. Recording on the device is not
> an option, since there's several operating systems involved.


Try using a VGA-to-composite converter and a video capture card. Or if
you're lucky enough to be using a VGA chipset with TV-out, enable that
feature.

But the quality will be rather low. The problem is that VGA - and I
assume you probably mean something better than baseline VGA 640x480
HS=31.5kHz VS=60Hz with only two intensities per color component, too -
has an awful lot of bandwidth. Yes, you could design a system to
capture it, but it's a lot of work because you'll also need to compress
it in realtime.

 
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Paul Carpenter
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      09-21-2005, 06:26 PM
On Wednesday, in article <(E-Mail Removed)>
(E-Mail Removed) "Wim Godden" wrote:
>I'm looking for a way to connect a VGA output to a system, so we can


Do you mean a real VGA or a computer system video o/p at ANY resolution?

>record whatever the user is doing. We would use a split-system to split
>between the user's own monitor (actually a beamer) and the recording
>system.


Why would you need to show the recorder for?

Anyway screen capture even at a low res of 640x480x nbits is still RGB
running NON-interlaced at 60Hz and just capturing it will use a lot of
bandwidth (system and capture interface). Then displaying it SCALED on
another monitor will use a lot of computation time and more system
bus bandwidth continuously transfering to screen.

Then there is the computations to compress the data (continuously) and more
system bus bandwidth used transferring the data to a storage device.

Real time video processing is HUGE amounts of data CONTINUOUSLY and
systems from security surveillance to TV studios uses DEDICATED hardware
especially when it comes to multiple sources.

>However, we have no idea how to record a VGA signal. Can we use
>3 analog inputs combined to reconstruct the image, then save it as a set
>of JPEGs ? Or are there easy conversion systems ?


OUTPUTs can be combined into a video signal NOT suitable for video recorders.

For EACH display that needs to be captured a separate SYSTEM would be required
with a frame grabber SPECIFICALLY designed for that resolution RGB capture
preferably with ONBOARD (to the frame grabber) compression HARDWARE!

That data is then transferred as compressed files to a storage device.

Even compressed you will need a VERY large storage device! Do the calculations
to start off with RAW data at 640 x 480 x 24bits (what you would get from
a frame grabber) repeated 60 times a second for 10 seconds and realise
the MB that becomes

52.73MB per second uncompressed
527.3MB for 10 seconds uncompressed

Even if you manage a good compression of 1/4 it will still be large and
a large computational overhead to compress it.

Alternatively as has been suggested do a lower resolution record to video
recorder via a VGA to NTSC/PAL[1] converter to make a standard signal.
The resolution will either be grainy or potentially distorted.

If this data is then to be transmitted over networks you will need
SEPARATE networks as point to point for MULTIPLE grabbers if you want
60 frames per second.

[1] Depending on where you are in the world.

>We would need to make it as small as possible, so PC/104 or similar
>formats are advisable.


Define as small as possible as the amount of data storage is huge, so will
need some chunky storage means.

Alternatively work out how many updates you ACTUALLY need as a lot of the
time the data will be the same! Consider either grabbing every 5th or 10th
frame to store, to reduce overhead.

Consider that even time lapse recording uses special hardware to SWITCH
between cameras to record multiple sources, and does NOT pass the video data
through a computer at all!

Another alternative is to look at VNC type network software to capture the
screen using forced to 8bit data and only sending CHANGED information, and
writing your own software to process the data and store it.

Real time video processing is a lot harder than connecting a camera to
a computer. There are serious bandwidth and computation overheads to be
considered and NOT a single byte can be late or delayed.

One system I designed for 3D RGB processing had an effective 2.5GIPs
continuous processing at upto 32 bits wide on each R, G and B with

48 multiplies
12 adds
various pipeline stages (limits, rounding, LUT)

All happening on EVERY clock cycle! Total system delay time including
conversion from interlace to non-interlace 19 PAL TV lines input to output!
That is 19 x 64us = 1.216ms ! No PC/104 processor or many larger processors
could achieve that.

If you are really serious and need design effort from someone with 20 years
of working in real time video processing, to computer based image processing
then email me. I think you have bitten off more than you can chew unless
you have a more detailed specification already, a detailed specification
and processing/bandwidth calculation needs to be done.

>Any help most appreciated !
>
>Kind regards,
>
>Wim


--
Paul Carpenter | (E-Mail Removed)
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate

 
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Paul Carpenter
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      09-21-2005, 06:58 PM
On Wednesday, in article <(E-Mail Removed)>
(E-Mail Removed) "Wim Godden" wrote:
>larwe wrote:
>
>> > I'm looking for a way to connect a VGA output to a system, so we can
>> > record whatever the user is doing. We would use a split-system to split
>> > between the user's own monitor (actually a beamer) and the recording
>> > system. However, we have no idea how to record a VGA signal. Can we use

>>
>> You can use a VGA-to-NTSC converter and record it on videotape.
>> However, it's much more efficient to record the operations of the
>> device that's generating the VGA output, and reconstruct the output by
>> simulation later.

>
>The idea is to record mutiple systems and store it on a computer system, so
>it can be downloaded by others on an intranet.


It that case you will need multiple point to point networks or a very
good streaming (multicast) protocol and client software to deal with it as
the intranet will be maxed out easily if you use multiple sources.

>Recording on the device is not
>an option, since there's several operating systems involved.


JPEG or MPEG files are supposed to be operating system NEUTRAL!

You will need to store some of it somewhere to at least buffer it up before
sending to the intranet.

It seems to me that either you send only one frame in 'n' or get some
form of video distribution system installed.

>Any suggestions ?


How many is multiple?

How many updates a second do you need?

What resolution are ALL the outputs to be 'recorded' running at?
This is VERY VERY important.

--
Paul Carpenter | (E-Mail Removed)
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate

 
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Clifford Heath
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      09-22-2005, 06:03 AM
Wim Godden wrote:
>>You can use a VGA-to-NTSC converter...

> The idea is to record mutiple systems and store it on a computer system, so
> it can be downloaded by others on an intranet. Recording on the device is not
> an option, since there's several operating systems involved.


I've always wondered why there isn't a record facility in a VNC
client. VNC is available for most operating systems, and the
protocol is documented, source code for both clients and servers
is available. You might create a VNC recorder and make a few bucks!
 
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sivadnz
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      09-22-2005, 09:41 AM

Wim Godden wrote:
> I'm looking for a way to connect a VGA output to a system, so we can
> record whatever the user is doing.


I've used a very nice system from MediaSite http://www.mediasite.com
which records the VGA output and a video
(composite/SVideo/Firewire/USB) feed from a camera, have a look at some
of the show case presentations at the Mediasite Website.

The mediasite gear was all automatic, just point the camera at the
presenter, connect the presenters Laptop (wheter it be
Windows/Mac/Linux) into the VGA capture card, and press RECORD, an
instant richmedia presentation.

The Mediasite gear used the following VGA capture card, check out
http://www.datapath.co.uk/visRGBPRO.htm this comes with software that
detects changes in the picture and creates a new Jpeg slide. I think it
even streams it to the web.

Alec

 
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Richard H.
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      09-22-2005, 02:04 PM
Clifford Heath wrote:
> I've always wondered why there isn't a record facility in a VNC
> client. VNC is available for most operating systems, and the
> protocol is documented, source code for both clients and servers
> is available. You might create a VNC recorder and make a few bucks!


The web conferencing companies have exactly this capability - whatever
you "share" off your desktop for a web conference can be recorded and
played back later, generally available as a freestanding file for use
independent from their service.

It's common to record a training presentation & slide show with their
tools and then use it elsewhere. IIRC, the file is in a standard
format, so as long as a reader is available it can be viewed on multiple
platforms. Java is often used for these client-side modules, so the
recording might even support multiple platforms too.

Richard
 
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Clifford Heath
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      09-23-2005, 04:55 AM
Richard H. wrote:
> The web conferencing companies have exactly this capability


Exactly - we use them regularly. That has nothing to do with
my comment that the open source tools should have a record
and playback facility. They have all the hard stuff already!
 
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