Why do you want a period capture device? They are crap in terms of quality when you compare them to what exist today. The marked for period capture device are very limited. The two I know about are the Matrox Mystique Rainbow Runner module and a Creative product which I don't remember the name of atm, but was mentioned in a 95-96 issue of CGW.
The Rainbow Runner module works in the same way as a USB capture stick that you can get on Ebay for a few bucks. Input signals are composite and S-VIDEO. This means you need to have a video card with TV-OUT capability. There can be loads of problems in DOS with this method as it is no guarantee that the card will output every resolution and refreshrate so that the capture card can process it.
The other card is from Creative, but works on VGA signals. I don't know how rare this card is, but according to the article in CGW it just worked on some games/resolutions. On both these cards you will need two computers, one to run the game to output the videosignal and one to record.
Edit: Here are the Creative products: http://web.archive.org/web/19961221173834/htt … o/ps_video.html
As you need two computers I don't see why you want to use a period capture device. These old machines can't do both, there just aren't enough CPU power to do it in an acceptable quality. The possible bitrates and hardware accelerated encoding is minimal and quality and framerate suffers.
Actually framerate is the worst problem when using software capture programs on old computers. When I tried to use a software capture program on my my 1.4 ghz P3 I could just capture in 11-12 frames from a program that was running in 30 (frame limit). Also those programs only work in Windows.
As you may see if you want to use period devices, then don't expect very good quality, not compared to what else is out there on Youtube. If you want to be serious about it, getting a Avermedia VGA (or similar) HD capture card is the only way to go. I've also made a thread here on Vogons on how to capture unsupported resolutions and refreshrates on the card.
Capturing the VGA signal gives a much better quality than with S-VIDEO. Before I managed to capture the VGA signal I did some tests with S-VIDEO. Here is a short clip of Destruction Derby on the S3 Virge captured using S-VIDEO: http://www.youtube.com/watch?v=6RA8WHP3QFY Then compare that to my comparison video captured with VGA: http://www.youtube.com/watch?v=DFVcYvOvCrs. Bitrate and capture framerate is the same in both videos. The only difference is the source signal. Another advantage with capturing with VGA is that the signals are already progressive, but S-VIDEO is interlaced and thus will require post processing to get them deinterlaced, again more work.