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Recording VGA output ?

Discussion in 'Embedded' started by Wim Godden, Sep 21, 2005.

  1. Wim Godden

    Wim Godden Guest

    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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  2. larwe

    larwe Guest


    > 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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  3. Wim Godden

    Wim Godden Guest

    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
     
  4. larwe

    larwe Guest

    > > 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.
     
  5. On Wednesday, in article <>
    "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 |
    <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
     
  6. On Wednesday, in article <>
    "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 |
    <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
     
  7. 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!
     
  8. sivadnz

    sivadnz Guest

    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
     
  9. Richard H.

    Richard H. Guest

    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
     
  10. 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!
     
  11. koko

    koko Guest

  12. On Friday, in article
    <>
    "koko" wrote:

    >On Wed, 21 Sep 2005 13:12:42 +0200, Wim Godden <> wrote:
    >
    >http://www.alacron.com/downloads/forweb/FVIDEO4.pdf


    Whilst it might do part of what the original poster wants, it may also be
    overkill for his application (in budget terms as well). Last time I was
    involved with Alacron was interface to MRI scanner for a hospital to use
    in a mobile unit (big bus). That was a few years ago, when I was working
    for a company that was selling Alacron kit in UK, and I wonder if some
    of the guys I knew then from their previous company still work there.

    >or diy on AD9888


    Be interesting to see how the original poster plans to proceed.

    --
    Paul Carpenter |
    <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
     
  13. Alex Gibson

    Alex Gibson Guest

    "Wim Godden" <> wrote in message
    news:...
    > 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



    Use a video surveillance box(video server) from TV out or similar
    Most should be able to output motion jpeg or mpeg2 or mpeg4
    then just record on to a server. With mpeg4 it should be about
    4-8 Mbps

    Like an Axis 240 or 250
    http://www.axis.com/products/cam_241/index.htm

    Alex
     
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