Using computer output as a video source

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Contents

Introduction

There are various times when it can be useful to use the output of a computer as a video source, including

There are different hardware devices available, depending on the type of output connection available on the PC.

VGA

For VGA output, there are several low-cost options that can connected using a cable splitter so that the VGA output from a computer is routed both to a projector/second monitor, and to the screen grabber. Many of these use a simple USB interface into the VidBlaster computer.

Using an Epiphan VGA2USB device
Be aware that the frame rate of some of these USB devices can be quite low, especially at resolutions around 1024x768 or higher, and this may limit the ability to capture animations/screen transitions or videos at full frame rate.

There are higher cost options in the form of PCI cards that can be used to capture VGA output with a higher framerate, like the Startech PEXHDCAP or Magewell X1204XE.

Note - there’s a limit to the length of cable through which an analogue VGA signal can be run. In most cases it is better to put the frame grabber close to the presenter's computer, and use an active USB cable to connect the frame grabber to the VidBlaster Computer. Also consider the number of USB channels available on the VidBlaster Computer. There's a discussion on this in the article on connection types.

Examples of remote VGA capture devices:


Startech VGA2Vid converter
Another way of dealing with an analogue VGA output is to convert it to an analogue SD video signal (PAL or NTSC), and capture that into VidBlaster rather than the raw RGB+Sync VGA signal. Once converted to analogue video, much longer cable runs can be used over standard co-axial composite video cable. Another advantage of this method over using USB VGA capture devices is that they work at full frame rate.

Examples of VGA to SD video converters:

An unbranded VGA to HDMI converter
It's also possible to convert VGA to a digital HDMI signal, which potentially covers both SD & HD resolutions at full frame rates, depending on the spec of the converter. However, compared to analogue video or SDI, HDMI is not suitable for longer cable runs (eg more than 15M), although cable construction can vary - along with the results.

Examples of VGA to HDMI converters:

DVI

For DVI output, there are products available that can convert the DVI output into analogue video or an SDI video stream. These devices can handle normal video frame rates, and the resulting SDI stream can be run over longer distances to the VidBlaster computer, typically 50-100M or more.

Matrox Convert DVI
Examples of DVI conversion devices:

Examples of SDI capture cards:


DisplayPort

DisplayPort is a digital output, used among others on Lenovo Laptops and Apple Macs. There are low-cost adapters/cables available that can convert DisplayPort output into a HDMI stream. Make sure you get an active adaptor (not a passive one).

HDMI

IntensityPro.jpg
HDMI is getting increasingly popular with newer laptops and video cards on desktops. Many DVI outputs are also capable of generating HDMI-compatible output via a simple passive adaptor/cable. There are also projectors with HDMI input that are coming into use.

There are HDMI splitters available so that the HDMI output can be sent both to a projector/monitor and to a capture card in the VidBlaster computer. HDMI capture cards allow for high frame rates at HD resolutions, but there are limits on maximum HDMI cable length because it was designed for domestic/consumer installations. For professional environments, HD-SDI is the preferred signal format, allowing for much longer cable runs over single-core coaxial cable.

Examples of HDMI Capture cards:

See also - Using desktop capture software and LAN cabling for Streaming a remote desktop into VidBlaster.
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