Computing@Thayer

As I described in a previous blog post, “Video Recording with Synchronized Slides“, we use a Canopus TwinPact 100 framegrabber to capture the presenter’s screen. This is recorded right along side video of the presenter speaking. The TwinPact 100 converts a VGA video signal to Firewire.

Recently I came across the Epiphan VGA2USB frame grabber. While simpler, it looked like it might shed features we don’t really need, while providing better video quality.  We decided to order one, and yesterday it arrived on my desk.  I decided to do a very quick side-by-side comparison with the TwinPact 100.

Here are some findings.

The Epiphan VGA2USB lacks features found on the TwinPact.   It only accepts VGA as input and USB as output.  The TwinPact has VGA, Composite, S-Video, and Firewire based input and output.  It also handles audio. Other than the audio, we’ve never had the need to use these alternative inputs.

The lack of additional inputs and outputs means the VGA2USB is much smaller.  It also doesn’t need an external A/C adapter.  It gets power from USB.

The biggest reason for my interest in the VGA2USB is quality (sharpness, color, contrast) of the video.  We often have presenters that put tiny text and diagrams on their slides.  Such items are usually not readable with the TwinPact 100.

To compare the two frame grabbers, I connected the outputs from both the VGA2USB and the TwinPact 100 to a MacBook Pro Core Duo running Wirecast under Mac OS X 10.4.11.  I then connected the inputs to another Mac using a powered VGA splitter.

In Wirecast, I arranged the output video from each unit side-by-side, and set Wirecast to record an h.264 video at high quality at 1280 x 720 pixels.  Using these settings, the Wirecast Mac was only able to muster 6.5 frames per second, but for this test I’m not really interested in frame rate.

Here is the QuickTime video of the results.

I’ve pulled some interesting stills from the video…

Side-by-side comparison of a web page  - This shot shows the comparison of a web page with text and images. The Epiphan is clearly brighter and easier to read. For reasons I’m not sure, the video from the TwinPact is vertically squished.  The right side of the TwinPact is also cropped.  It is possible to do some basic resizing and positioning with the TwinPact remote.  The process is kludgy and if you plug in a different computer, the size and position often need to be fixed all over again.

Screen Motion comparsion - The biggest issue with the VGA2USB is that the video is interlaced. The interlacing is very visible for any motion in the incoming video (presenter moves a window, uses slide transitions, or shows a video clip). Epiphan does make other models of the VGA2USB with progressive output, but they start at twice the cost.

In the above comparison, you can see the quality of the text.  The Epiphan VGA2USB is on the top, the Canopus Twinpact 100 is on the bottom. The VGA2USB is much easier to read.

VGA2USB noise - In this image, you’ll see some noise from the VGA2USB.  Not sure if this is the problem with the driver, hardware, or something else.

There are some other possible issues with the VGA2USB.  At one point in the above video, the output appears blank. This along with the random noise I mention above  At higher resolutions, the frame rate on the low end VGA2USB model goes way down.

In our case, the benefits of a simpler and smaller piece of  hardware with higher quality video out make the VGA2USB an excellent new tool for our Wirecast recording systems.