slevy@poincare.geom.umn.edu (Stuart Levy) (11/13/90)
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@geom.umn.edu, (612) 624-1867sabbagh@acf5.NYU.EDU (sabbagh) (11/14/90)
In article <1990Nov12.193845.11889@cs.umn.edu> slevy@poincare.geom.umn.edu (Stuart Levy) writes: >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! We here at the Courant Institute have successfully made single frame recordings without a genlock board. Our equipment consists of: SGI Personal Iris Lyon-Lamb Color Encoder Vas IV video controller Sony 3/4" video tape recorder. I do not know any of the prices; I am just a mere graduate student and am listed as a peripheral myself :-). The basic technique is as follows: we take the RGB output from our personal Iris and plug it into the Lyon-Lamb's RGB input. This encoder supports sync on green without no jumpering or anything; just don't plug in a sync signal. Any IRIS using the suggestively named (???) de3 board to generate its video output for the monitor may be used in this fashion. Note that there is no way to view images on the video monitor and send them to the equipment at the same time. To switch from 60 hz hi-res to RS-170, with sync on green: setvideo(DE_R1,(long) DER1_170 | DER1_SYNCG); To switch back to 60 hz (so you can use your monitor again): setvideo(DE_R1,(long)DER1_60HZ | DER1_SYNCG); This works, and produces better picture quality than the composite NTSC output from the genlock board (suggestively named cg2). According to the documentation (???) provided by Silicon Graphics, the best possible output ("broadcast quality") is obtained by using the genlock board to receive an sync signal generated by your encoder. We have not tried this; when we do, we will post our results. The single frame recording is accomplished by treating the VAS IV controller as a tty; you send ASCII character sequences as commands, and it sends them back as status indications. This is connected through an RS-232C connection from serial port 2; make sure to chmod ugo+rwx /dev/ttyd2 for this to work. Hadil G. Sabbagh E-mail: sabbagh@cs.nyu.edu Voice: (212) 998-3125 Snail: Courant Institute of Math. Sci. 251 Mercer St. New York,NY 10012 " There's a difference between being hungry, and being on a diet." - Commentary about John Cougar Mellenkamp. Disclaimer: This is not a disclaimer.
mike@BRL.MIL (Mike Muuss) (11/22/90)
In a recent note, Stuart Levy writes: >> 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. ... This is somewhat misleading. 3/4" U-matic tape is also recorded as separate luminance (Y) and chroma (C), as is regular VHS, Super-VHS, and many other formats. The differences between these formats are in terms of bandwidth available for each signal, and signal/noise ratio. While some very low-budget operations have begun mastering on S-VHS, there is no question that S-VHS is a lower quality format than 3/4". A 5th or 6th generation dub on 3/4" is still of acceptable quality (although not prizewinning), while the same can not be said of even a 3rd generation S-VHS dub. Certainly not with any S-VHS equipment that I have worked with. It is important to note that the Y/C bandwidths on 3/4" come in two flavors as well. Regular 3/4" has about 260 lines of resolution (e.g. about 520 pixels/scanline), while SP-format 3/4" has about 360 lines, or about 720 pixels/scanline. The NTSC format is bandwidth limited by law to have no more than 720 pixels/scanline, so this is as good as it gets in real NTSC. Wider bandwidth signals can be easily created in your studio (the "multiburst" signal from most test sets is an example), but it isn't real NTSC. Thus, the SP version of 3/4" fills roughly the same need for 3/4" users that S-VHS serves for VHS users, but with the 50 dB video S/N and tape speed stability of the 3/4" format. A QUALITY COMPARISON: Subjective, and Measured. Just last week, I had the opportunity to make several dubs of my recent video, and used this chance to compare S-VHS to regular (not SP) 3/4". I tried to give the S-VHS dub every advantage. I used my NEC 1000 S-VHS machine ($1000), which I have measured as having about 375 lines of resolution in S-VHS mode (i.e., full NTSC bandwidth) on the composite NTSC input. Note that the manufacturer claims this machine to have "425 lines of resolution" when fed a non-band-limited S-Video (Y/C) input signal (which is hard to come by). I connected the output of the 1" mastering machine directly to the composite NTSC input of my S-VHS deck, and used TDK's best S-VHS tape. Hi-Fi sound was also taken straight from the 1" machine. (BTW, 1" machines have rather mediocre sound, ~45 dB S/N, compared to better than 80 dB S/N on a Hi-Fi VHS or S-VHS deck). Next, I also made a copy on 3/4", through the regular distribution amps, i.e. I had additional gunky circuitry in the signal path over the S-VHS dub. Comparing my S-VHS dub to the 3/4" dub requires no special talent. The S-VHS copy is *much* noisier than the 3/4" copy. And recall, this is conventional 3/4", *not* the wider bandwidth SP format. The S-VHS is still quite good to look at, but not nearly as nice as the 3/4". If you are accustomed to viewing NTSC only on VHS tape, you would not be upset, but if you are accustomed to viewing NTSC as it exists in the mastering process, you would mourn the loss. However, it is true that 3/4" is no longer the best way to capture video. In order of increasing quality, the competition comes from Hi-8, Betacam SP, D-2 digital, and D-1 digital. Betacam SP is a "component" video system, recording Y, R-Y, and B-Y signals, rather than Y and C. D-2 is a "composite" (Y/C) digital format, and D-1 is the "component" (Y, R-Y, B-Y) digital format. D-2 decks are now available for less than $50k, and the prices are comming down. Since a good 3/4" machine costs from $10k to $30k, this isn't such a large price difference (reference: the Sony BVU-850 and BVU-870). Note, however, that while the digital formats offer zero generation loss, the digital format has inherrent quantization, which can be quite noticable in the D-2 format. 8 bit samples are just not wide enough; we need 10 or 12 bits to satisfy the discerning eye, even with dither used to prepare the original signal. Mind you, I'm no big fan of NTSC -- it is a very limiting, low quality video format. But, it has supplanted 16mm film (a superior quality format) as the standard way of communicating scientific results, so one might as well understand it, and master it. NTSC, when done well, can be a very striking and effective way of communicating. AN EXAMPLE OF MAKING A VIDEO Just to give you a quick idea of how I created my recent video: Images were created in RGB at 1280x960, and decimated using a 5x5 filter kernel down to 640x480. These RGB images were converted to Y/U/V format, the U and V data was low-pass filtered to meet NTSC bandwidth limitations, and the YUV data was transmitted over Ethernet to an Abekas A60 digital video disk ($60k), where they were stored in D-1 digital video format. When an entire segment of video had been loaded onto the Abekas, it was played back in real time, under control of an FCC-approved broadcast quality sync generator. The RGB outputs of the Abekas were sent to a Faroudja CTE-1 RGB->NTSC encoder ($7k), and the composite NTSC was recorded on a Sony BVU-870 3/4" VTR ($30k) with SMPTE time code generator. Real-time sequences were captured from an SGI-4D/240 GTX ($100k) with CG3 board ($7k?). The sync pulses were fed into the CG3. With the SGI in NTSC mode, genlocked to "house sync", it provided RS-170 RGB, which was fed into the Faroudja encoder, and the composite NTSC was recorded on the BVU-870. I note in passing that the CG3 still does not succeed in producing broadcast quality video, although it is far better than earlier attempts. Unlike earlier SGI CG boards, the output of the CG3 is sufficiently good that it can actually be used, if you don't mind "tweeking" the Faroudja into forgiving SGI's sins. Each segment went onto a separate 3/4" cartridge, and all were indexed event-by-event according to the time codes. This allowed the script to call for segments to be assembled with individual frame accuracy. (Allow me to make a BIG PLUG for the use of SMPTE time code on your video tapes. It makes the editing process vastly easier, and more accurate). All the 3/4" original tapes went into a big box, and I took it all to our 1" edit suite. The original tapes were read on a pair of Sony 3/4" machines (VO series), stablized by a time base corrector (TBC), routed through an edit controller with Ampex effects box (for fades and wipes) and Ampex ADO (for inset screens, flip-away effects, and "MTV" style rotating and tumbling images), after which each finished sequence was recorded on an Ampex 1" machine ($50k). After the video was complete, I added the music to Channel 1, going from Compact Disc to the 1" machine via a sound board, where the mix to mono was accomplished. Then, I recorded the narration in a sound booth, onto a 3/4" tape. Using the same edit system, the narration track was copied onto the 1" machine (although I'm proud to say that in 8.5 minutes of narration, I only made one "flub" that we had to splice in a replacement for. This was done using the edit system, just like editing video). At this point, the master tape was finished. Dubs for the final distribution were made from the 1" master onto 3/4" and VHS, through a 1->12 video and audio distribution amplifiers. Thus, the distribution copies delivered to the clients are only 3rd generation. Since the trip from 3/4" to 1" is "nearly lossless", the distribution copies have excellent quality. Given that, in my instance, distribution is done on 3/4" and VHS, increasing the quality of the intermediate steps is not likely to make a noticable improvement in the quality of the product. The 1" master would be completely suitable for broadcast. Even if you don't have the financial resources to engage the services of a 1" edit suite for your video productions (not that it is very expensive), and you do all your production and editing in 3/4", you will get a high quality result. Certainly better than anything you could produce on Super-VHS. FRAME AT A TIME In the past, I have also done quite a bit of frame-at-a-time recording of video, using the Sony 3/4" machines and a Lyon-Lamb VAS-4 VTR controller. This produces results of equal quality (all other elements being equal), but takes longer. It is also more of a bother to find and fix botched frames when recording this way. It also requires a much smaller investment in equipment! ($5k for Lyon-Lamb Mini-VAS, plus a VTR). LASER DISCS On a related topic that I won't bore you with this evening, I recently investigated the quality of LaserDisc players. They are much better than consumer videotape (even Beta), but 3/4" tape does even better. The machines evaluated were the Pioneer CLD-91 ($2000) and Pioneer CLS-S2 ($3500) [the worlds finest Laser Disc player at the moment]. SUMMARY *) 3/4" videotape is no longer the best thing around. *) 3/4" can be used to produce excellent results. *) 3/4" beats S-VHS every time (video, not audio). *) 3/4" is mature, and not too expensive. Many alternatives exist, and lots of good stuff is happening. Keep your eyes on Betacam SP and D-2. If you have (or are) a good video engineer, there are lots of alternatives. If you don't have access to a good video engineer, the business of video recording still has a lot of pitfalls, and it will pay to be very conservative. Be suspicious. Also, most large universities and companies have a TV studio, and there are many commercial firms in the business. Strongly consider using them to assist with your post-production needs. The aid of a professional video editor (person) can greatly increase the quality of your result; knowing when and how to use fades, wipes, etc, is more of an art than a science. Rates are generally in the $100/hour to $200/hour range, and often less. Best, -Mike Muuss PS: In case you are interested, all the image generation software, image filtering software, Lyon-Lamb controller software, etc are all included as a small, but significant, part of the BRL-CAD Package, which we make available for free. See SGI's software partners catalog for details, or send E-mail.