Single-frame video recording from an Iris

[Stuart Levy]

Several people have been asking about video recording off an Iris, so thought
I'd describe our setup.  We have

   an Iris (4D/240 GTX) with genlock board,
   Diaquest series 2/20 single-frame videotape controller (~$5K),
   JVC BR-S811U super-VHS single-frame editing videotape deck, (also ~$5K)
   Sierra Video Systems  RGB->Y/C (luminance/chroma) transcoder (~$1.2K),
   JVC 1400-SU super-VHS monitor (~$650).

(Actually we also have another tape deck and a controller for tape-tape
editing, but the above suffices for single-frame recording.)

>From what I hear, super-VHS is supplanting 3/4" tape.  (In fact, JVC and
Panasonic are discontinuing their 3/4" lines.)  SVHS uses Y/C component video,
with two channels on the (1/2") tape, one each for luminance (Y) and chroma (C)
plus the usual audio stuff.  SVHS is supposedly higher resolution than 3/4"
but somewhat worse noise.  The difference is apparently not large, but
SVHS equipment is decidedly cheaper.  Note that SVHS equipment can play &
record in VHS mode too (at lower quality); VHS equipment can't play SVHS
tapes at all.  SVHS tape decks do output vanilla NTSC as well as separate Y/C
signals, so with two decks you can make VHS copies.

This setup works quite well for us.  The transcoder's video output is much
sharper than the NTSC-encoded output from the genlock card, and also much
better than that of a (cheap) external RGB->NTSC encoder we tried.
Good RGB->SVHS (separate luminance/chroma chroma) transcoders also seem much
cheaper than good RGB -> full NTSC encoders.

We had to write some software to display frames and send commands to the
Diaquest controller -- anyone interested in this please let me know.

The only annoyance is that our Iris' console is taken up while we're recording,
since we have to switch it into RS-170 mode (NTSC scan rate) which the SGI
monitor naturally doesn't handle.  The recorded area is about the lower left
640x480 pixels of the screen, less overscan.  We're thinking of getting SGI's
Video Creator (?) board so we can record without tying up the display.

It *might* be possible to live without the genlock board altogether.
We run the Iris as the master sync generator, and as far as I can tell,
the genlock board isn't giving us much except a separate sync output.
We should be able to use the Iris' built-in video generator -- the one
that's switched by ``setmonitor(NTSC);/setmonitor(HZ60);'' and have the
sync-on-green signal drive the rest of the video equipment.  The Sierra Video
transcoder has a (solderable?) jumper option to use sync-on-green, and the
other hardware might work with it.  I haven't tried this however!


(I have no connection with any of the companies mentioned above except as a
satisfied customer.)

    Stuart Levy, Geometry Group, University of Minnesota
    slevy at geom.umn.edu, (612) 624-1867