I've noticed a lot of people record their SGIs by filming a monitor, especially 13W3 SoG (Sync-on-Green) systems. I always use my SGIs through a capture card even when I'm not recording, so I wanted to share my experience a little bit.
Since most capture devices don't mention whether they support SoG, I spoke to somebody who develops frame grabbers (that's just an expensive term for capture card). He said "that's done by the Analog Devices chip"; the card manufacturer has little control over whether SoG is supported, you have to check the data sheet of the ADC the card is using. Unfortunately, which ADC a card uses is not always disclosed.
I use an
AVerMedia DarkCrystal HD Capture CD530. This has the added benefit of audio input. Normally this card is quite expensive, because it is intended for professional use. Luckily I got mine on eBay for ~200 CAD; not cheap but I think worth it. I selected this card primarily because they advertise high signal compatibility (including the resolution adjustment tool which has some advanced sync settings), as well as the fact that it handles both analog and digital inputs.
The ADC in this card is an
Analog Devices ADV7604, information that I don't think existed on the internet previously (AVerMedia doesn't mention it). They seem to be doing something fancy with it, probably to do with lower color-depth, because they list a maximum supported resolution of 1920x1200@60 which is higher than what Analog Devices lists (though reasonable given the chip's pixel clock of 170MHz). Plenty for capturing an Indy; you could even capture at 75Hz if you really wanted. In the datasheet for the chip, you will note that they use the term "embedded synchronization" more often than SOG, so that is a phrase to look for. It is apparent that oddball sources with embedded sync were considered heavily in the design of this chip.
To this particular card: It works perfectly with my Indigo 2 (GR2). I do get some odd behavior on my Indy (XL24) before it fully boots into IRIX: the image appears slightly squished in width, and when the video drops out for a moment (say when going from the splash screen to the "system is coming up" screen) it loses sync and I have to disable and re-enable to device to get sync back. This is trivial in the included capture application, but slightly annoying. Regardless, once IRIX fully boots I haven't had any issues.
I should also say, I have yet to get the resolution adjustment tool to work. It says "can not detect the format file!!", which I think is engrish for "cannot get lock on the input format". I have never tried it with a "normal" source, so I can't comment on if it is just an issue with embedded-sync sources. There is another adjustment tool that works properly for specifying V-Hold and H-Hold (as well as some other things).
Does anybody else have experience with capture cards and SoG SGIs? If so, it seems useful to keep a record of which ones do and do not work.
![[Image: GIMP.png]](https://hallmonitor.ca/wp-content/uploads/2020/03/GIMP.png)
P.S. If the image is resized by your browser, it comes out a bit soft. If you click through to the full image, you can see it is very crisp for analog video.
