HIGH DEFINITION VIDEO RECORDING FORMATS
As your present analog and digital video recorders grind themselves into retirement, you may be wondering what format the next round of VCRs need to be. Perhaps your postproduction facility, school, or business is gearing up for the coming of HD (High Definition) or perhaps you are a broadcaster feeling the hot breath of the FCC with its impending requirements to broadcast in DTV. Of course you could stick with the present standard definition (SD) gear and using an upconverter, change whatever you are using now to "pseudo HD", something with the data structure of HD but lacking the true high definition. Or, maybe you will go all the way, forging a path onto the nascent landscape of high definition television recording.
Whatever you do, the coming HD revolution is likely to make pioneers of many of us. It will be easy to tell which of us were the pioneers; we'll be the ones with the arrows in our backs. That's because the decision to move into HD will be expensive and dangerous. The list of what's available and how much it costs will change rapidly making almost any decision you make a short term one. Put another way, whatever you buy, needs to be supported by a business plan that shows heavy use of your HD purchase so that it can be amortized over two or three years. Let me put it still another way, because this is important. Your HD recorder will cost between $40,000 and $100,000, based on what's available today. As new products reach the market, competition will drive some of these prices down. If a gizmo you paid $80,000 for today can be replaced by another gizmo that costs only $40,000 two years from now, you'd better have a plan to work the heck out of that $80,000 gizmo if you want to compete two years from now with your neighbor who will then be buying a $40,000 gizmo that's better than yours.
Although this is an article about formats, it's not very instructive to compare technical specifications like track length and data rates. These riveting tidbits are available through SMPTE at smpte.org. It's the implementation of the format that counts, so let's see what the VCR manufacturers are doing.
Some generalities about HD recorders
You have three kinds of recorders out there;
the expensive, no-holds-barred, high bit rate recorders that suck
up data with wild abandon, you have the the newer HD recorders,
and you have the common SV recorders like DVCAM, DVCPRO50, D-9,
The top-of-the-line recorders (i.e. D6, HDD1000) can handle HD but are too expensive to be practical.
The SD recorders don't have a chance of recording all that data unless you compress the beegeebers out it. It can be done, though. Just slap an encoding processor onto an SD machine and squash away. Although this sounds like a bad solution, it's not so bad if the SD machine started with a high bit rate. Panasonic's D-5 recorder, for instance, records 235 Mbps uncompressed SD CCIR-601 data. It's not a huge leap to add a processor to the existing D-5 machine and squash the raw 1.5 Gbps HD data down to 235 Mbps, making an uncompressed SD recorder into a compressed HD recorder.
Other popular solutions: speed up the SD machines (usually doubling the tape speed, head rotation speed, and bit rate) and also compress the data mildly. The combination balances between the expense of high bit rates and the sharpness-damaging artifacts of compression.
Who has what?
JVC offers D9-HD based on its D9 (also called Digital S) format VCR.
Second in JVC's HD arsenal is W-VHS, an analog component video recorder/player used primarily for playing HDTV recordings.
Another format, D-VHS, is designed primarily for recording and playing back pre-encoded MPEG-2 data streams like you might get from a satellite receiver. JVC and Panasonic sell it.
Sony offers two HD video production formats, the HDD1000 1" reel-to-reel studio recorder that handles uncompressed high bit rate data, and its more affordable and more popular HDCAM.
Panasonic offers three formats, the high end D5-HD, a high bit rate studio deck modeled after the D5 format, and its more moderately positioned DVCPRO-HD, modeled after its DVCPRO (also called D7) line. Panasonic also offers a D-VHS deck.
Let's take a look at these formats one by one.
The D9-HD format offered by JVC is modeled after its D9 (Digital S) recording system. They are switchable between 720/p60 (720 scanning lines per picture, progressively scanned, 60 times per second and 1080i60 (1080 scanning lines per frame, interlaced with 540 lines per field every sixtieth of a second), as well as 1080p24 (1080 scanning lines per frame, progressively scanned at 24 frames per second with each frame containing 2 fields with 540 lines each). According to Dave Walton, D9-HD is "designed to be a cost-effective high quality digital recording format that offers practicality that one would get with an SD format. For example, with a D9-HD we have a recording time on camcorders as well as studio decks of 62 minutes.
"The logical comparison with any six
millimeter format is going to be regarding the amount of data
you could put on a tape. We use ½" metal particle
tape and ½" tape gives you the ability to record essentially
more data and have longer record times. It also provides backwards
compatibility with D9."
The D9 HD compression scheme is DCT (Discrete Cosine Transform) and uses a mild 3.3:1 intraframe compression. Although some manufacturers list a luminance and chrominance bandwidth for their HD VCRs, JVC does not. As Dave Walton explains, "The D5 machine has no analog inputs or outputs on it. Therefore, you can only feed a digital signal into it which doesn't have a bandwidth associated with it. If you are looking at the encoder or decoder that's used, then you are not measuring the frequency response of the video deck but the frequency response of the encoder. If you use the same encoder with a D5 machine as you used with the D9 machine or HDCAM, you'd have exactly the same spec, if in fact the sampling frequency of the video and audio were the same. The only difference would be in the compression algorithm. In D5, for example, it's a DCT based compression of about 4 ½ to 1. An HDCAM has a compression ratio of 7 to 1. But they are both recording the same sampling frequency of 74.25 MHz (MHz). So the difference is not in frequency response, the difference is in how much degradation takes place in the compression algorithms. The sampling frequency is fixed, thus the inherent resolution is fixed."
JVC's ½" metal particle video cassettes are modeled after a VHS cassette shell and cost about $45 for a 62 minute DS-104 cassette. JVC points out that 62 minutes is a long recording time for a standard sized cassette. The small camcorder cassettes used by HDCAM and DVCPRO-HD run 40 and 46 minutes in length respectively. The other formats require a large cassette, inappropriate for camcorders (to get recording times up to 124 minutes).
The D9 format can record up to 8 editable 16 bit audio channels.
[See Compression vs. Picture Sharpness for related information]
D-VHS is the digital version of VHS capable of recording MPEG-2 data like the kind transmitted via a satellite and will be transmitted by DTV broadcasters. As explained by Dave Walton," The D-VHS format is able to record 28.4 megabits per second on a standard oxide VHS-like cassette that sells for about $8. This adds up to about 45 Gb (gigabytes) or nine times the capacity of a DVD that can be recorded on a D-VHS cassette. Put another way, you can record a 3 ½ hour HDTV movie with the full HDTV quality on one cassette. The D-VHS machines would provide forward and backward compatibility with VHS machines already in use. There are a billion people now who have VHS machines and libraries of this material that they will be able to view 10, 15, or 20 years from now."
The D-VHS format is a marriage of two things: tape speed (which is proportional to the amount of data that is recordable and inversely proportional to the length of recording that can fit onto a tape) and the amount of MPEG-2 compression used. For instance, a high definition MPEG-2 data stream with reduced compression would require the machine to run at its fastest speed, recording maybe two hours at 28.4 megabits per second. A more compressed HDTV signal transmitted using the FCC mandated bandwidth of 19.4 megabits per second would permit the D-VHS VCR to record at a slower speed, recording 3.5 hours of an HDTV signal (but with more artifacts and less quality because of the increased compression). MPEG-2 can be adjusted to very high compression rates permitting as much as 49 hours to be recorded on a D-VHS tape. Thus the D-VHS format is extremely flexible allowing a wide range of image qualities and record times.
The D-VHS machines cost about $1000 and a 300 minute DF-300 cassette costs about $8 making D-VHS a very affordable way to store HDTV once it has been encoded. Although previous models required external encoder/decoders, JVC is now introducing models with built-in encoder/decoders with IEEE 1394 inputs/outputs.
D-VHS machines are not production recorders as the data has been far too compressed (using interframe compression) to be editable.
"I'm not sure what all the applications for that might be," says Dave Walton, "but it is reasonable to believe that there will be some applications in the production process for D-VHS machines whether it be archiving material off your hard disk or long recording times for DTV material. D-VHS is a long term format for both standard and high definition recording. The original designation of this format as simply nothing more than a 'bit bucket' has somewhat changed since the announcement in Japan of the D-VHS machines with built-in MPEG-2 coders and decoders. The bottom line is that a D-VHS machine is a VHS-type machine at extremely low cost that is specifically designed to record formatted MPEG-2 data whether that MPEG-2 data is created in the machine or supplied externally. But MPEG-2 has been decided upon as the transmitted DTV format so this recorder is designed to record and play that back at minimal cost and maximal benefits for the user.
"Our consumer division has been selling D-VHS format machines built into a dish network receiver for several years now. In the past couple of years, the only source of digital programming to the user at home has been through the satellite receiver. So, the only digital recorder practical for the home has been the D-VHS machines built into the satellite receivers that let you record and playback the signal you were receiving from the satellite."
JVC's W-VHS format
Unlike the other formats, W-VHS is analog, recording and playing the standard Y/Pb/Pr video component signals used by HD VCRs, monitors, and set top boxes. JVC is presently marketing the $4795 SR-W5 model and the $5950 SR-W7 model, the latter having BNC connectors and time code. W-VHS can record high definition 1035i, 1080i, or 1125i component analog signals. W-VHS machines can record or play regular VHS tapes, but when used with the high grade WT-120 ($65) or WT-180 ($80) metal particle VHS-like cassettes, the W-VHS machines can record and play the higher definition signals. Although they are not meant to be editors, the W-VHS models have assemble edit and audio dub capabilities and a VGA output for use with computer monitors.
According to Dave Walton, W-VHS "is an outstanding distribution format. We have corporations that pay megabucks to have large screen productions made for corporate meetings. Advertising agencies want to be able to view commercials. Even people in the home theatre environment may want to record a high definition football game in the home. What are their options? The fact is it'll plug into any DTV desktop box and record your game, it will plug into any HD camcorder, it will plug into any D5-HD machine. Y/Pb/Pr is the component standard, whether it's on a monitor or on a set top box.
" Another benefit of the W-VHS recorder is that we have provided a VGA output on the back so it can be plugged into a computer monitor so it can be used as an inexpensive HDTV monitor. "
Although W-VHS and D-VHS are both at the low end of the HD format spectrum, the two have about as much in common as lightning and lightning bugs. Both are backward compatible with existing VHS recordings but W-VHS is strictly an analog record/play mechanism while D-VHS is strictly digital. If you are starting with analog component video, you can feed it directly into a W-VHS machine. The D-VHS machine needs the video to be digitized and encoded (compressed) into an MPEG-2 datastream (internally or externally) to be recorded.
DVCPRO-HD is a production format on a par
with JVC's D9 and Sony's HDCAM. It is built on (and backward compatible
to) the DVCPRO format (which is also called D-7).
Panasonic will be offering two camcorders shortly after the first of the year, the AJ-HDC10 ($50,000) and the AJ-HDC20 ($65,000), the first having one million pixels per CCD and the second having 2.2 million pixels per CCD. (Camcorder prices are always quoted as list and without lens.) There is also a studio recorder, the AJ-HD150 ($65,000).
Although the camcorders operate in the 1080i (also 1035i ) domain, the studio recorder is a little different. According to Jeff Merritt, Panasonic's Product Marketing Manager for HDTV, "The HD150 is a native 1080i recorder but with an optional built-in universal format converter. The HD150 is playback compatible with all DV formats --- that's all DV --- That's mini DV, that's DVCAM , that's DVCPRO, 25, 50 megabit, progressive, any DV format. When using a format converter, it is possible to play back any of those DV formats, or DVCPRO formats and output either 1080i or 720p. "Not only is the HD150 studio deck compatible with all of the other DVCPRO and DV products on the market, it has eight channel digital audio capability and it's compatible with metadata and ancillary data recording. That's already built-in, it's not optional; that's part of the format. Metadata is data about data. Ancillary data is such things as closed captioning, it could be setup functions, it could be all kinds of other things, but they are pretty well clearly defined as not being data about data but being data by themselves. That is what is called ancillary data. SMPTE is working very diligently on making all of the standards of this stuff work."
Jeff Merritt goes on to say that the DVCPRO-HD format "... is is an extension of the entire strategy of Panasonic of not abandoning any previous formats but moving forward into newer technology with existing formats. In other words, DVCPRO25 was the first of the really large scale DVCPRO products to go virtually worldwide. And Panasonic developed the next version of that to deal with not only 25 megabit but 50 megabit 4:2:2 for example rather than 4:1:1. It is still backwards compatible with 50 megabit equipment, and backwards compatible with 25 megabit equipment. Now we get into 100 megabit equipment. It's still compatible with the 25 and 50 megabit stuff for playback. So we're staying with what works, with what has been accepted worldwide as a standard.
"The DVCPRO-HD VCRs are compatible with other manufacturers' DV products; you can even play back a DV tape made on a home DV camcorder. The advantage is for people who have already acquired a library in either the 25 megabit or 50 megabit DVCPRO material. That material is not obsolete, that material can now be repurposed by being up converted to the 1080i or 720p and mixed with other high definition material. "
DVCPRO-HD uses DCT compression like the other DV formats, but it is variable up to 7:1, depending on what's in the image.
The camcorders operate at 59.94 fps (fields-per-second) only, the studio model is switchable between 59.94 and 60 fps.
The format supports eight discrete 16 bit audio channels at 48 Khz sampling. The Panasonic camcorders are unable to edit these audio channels but the studio deck can.
Although the ATSC table lists 1080 x 1920 pixels for an HD picture, the DVCPRO-HD studio machine is only capable of recording 720 x 1280. You can feed it 1080 x 1920, but it records and plays back only 720 x 1280, with some pixels obviously manufactured by the machine. This "cheat" was necessary to reduce the data rate to the 100 megabits per second range manageable by the VCR.
Panasonic doesn't presently support the 1080p24 format with DVCPRO. According to Jeff Merritt, "it's under development".
One welcome surprise is that the DVCPROHD machines from Panasonic all use standard DVCPRO tape, so you don't have to stock another tape flavor on the shelf.
Panasonic D5-HD -
D5-HD is Panasonic's top of the line high definition format. D5-HD is a studio production format. The VCRs are studio consoles only, there are no camcorders. Although it is based on its standard D5 format, the HD machines will not play D5 standard definition tapes.
Jeff Merritt explains the background of D5-HD: "We have to take a look at the history of D5 and work up to D5-HD to understand what's going on here. D5, a SMPTE format, is uncompressed, what we call CCIR601. It is an integral serial digital component 4:2:2. Well, what we did was to take that basic format and married an AJ-HDP500 high definition processor with the D5 format and then were able to put up to 235 megabits on tape working in the high definition domain at 1080i." In other words, the DCT processor compresses the 1.5Gbps found in the CCIR601 uncompressed data stream down to the 235Mbps recordable on tape. "Now from there we incorporated the HDP500 processor into the next generation of the machine which became the AJHD2000 which has since been discontinued, replaced by the HD2700. Where this gets us is to: a strictly HD only machine, the AJHD2700 that's compatible with native 720p and1080i, full bandwidth 4:2:2. The original AJ-D580 machine still exists and we still sell many of them. As facilities are moving from analog to digital, they would like to go uncompressed and they can do that with the D5. We have announced a new tape machine whose model number is currently AJHD3000 that incorporates all D5 formats in one machine including D5, uncompressed CCIR601, 1080p24, 1080i 720p, all in one machine. It records and plays all D5 formats and an optional universal format converter can be part of the package."
Panasonic's first deliveries were in the summer of 2000. The AJ-2700 costs $99,000 as will its successor the AJ-HD3000. The AJD580 (standard definition D5) costs $72,000 and the AJ-HDP-500 processor costs $52,000. The combination of these two devices will make high definition video.
Panasonic's D5 HD machines, because they are based on the D5 format, work in the full bandwidth 10 bit domain (there's no prefiltering or postfiltering of the signal as is done with the Sony HDCAM. Also the HDCAM works only in the 8 bit mode.) Panasonic's D5-HD is also switchable to an 8 bit mode. While in that mode it uses a 4:1 intraframe compression. In its 10 bit mode, it uses a 5:1 intraframe compression.
The VCR is switchable between 59.94 fps and 60 fps.
As with the DVCPROHD studio deck, the new D5-HD VCR has 8 editable audio channels.
One thing setting the D5-HD apart from other formats is that it records a true 1920 pixels by 1080i image (Panasonic's DVCPROHD records only 1280 pixels and Sony's HDCAM records only 1440 pixels). It is also switchable to 1035i and 720p. One reason why the D5-HD machines can record such a detailed picture is that they're throwing 235 megabits per second onto the tape, (as opposed to DVCPRO-HD's 100 megabits per second, D9-HD's 100 megabits per second, and HDCAM's 140 megabits per second).
Who's using this format? Jeff Merritt explains, "It is the defacto standard of high resolution recording and playback for high definition. Every motion picture company, every high end posthouse in the Hollywood community and the New York community is working in high definition, virtually every broadcast network is recording or originating in HD. It is the delivery standard of choice for all of these people, the networks in particular including HBO. When you watch ABC Monday Night Football in high definition, you see instant replays done on D5-HD, on the HD2700, for example. This was the format chosen by the Lucas organization, Lucas Arts, to master the Star Wars Trilogy on."
Panasonic D-VHS -
Although DVHS, as mentioned earlier, is not a production format, it is still a high definition video recording format. Panasonic's PV-HD1000 costs under $1000 and is now available. It connects to a set top box which decodes satellite TV signals and feeds them to the VCR via an IEEE 1394 connector. The PV-HD1000 is essentially a "bit bucket" recording and playing raw data and doing nothing with it. When the data is played back, the signal is fed out through the IEEE 1394 connector back into the decoder which feeds the television via the set-top box. Unlike the JVC model, the PV-HD1000 has no MPEG encoders or decoders. Like the JVC model, it will record and play standard VHS and SVHS tapes. When recording MPEG-2 data, however, one must use D-VHS tape, a higher grade ½" metal particle tape similar to that used for SVHS.
The PV-HD1000, according to Jeff Merritt, is popular among broadcasters playing back videos in their lobbies.
HDCAM uses a Betacam-like cassette with metal particle tape but none of the present VCRs are backward compatible with Betacam, DVCAM, or other formats (this may come later). Presently available is the HDW-500 studio deck ($61,400), the HDWF-500 studio VCR ($69,300), the HDW250 portable deck (no price available), and HDW-700 one-piece camcorder ($78,800). All work in the 1080i native domain, but with an additional circuit board, the output can be converted to 720p. The HDWF-500 can record and play in 1080i and 1080p24.
There are four models of tape to feed the hungry HDCAM. Only the studio VCRs can take the BCT-124HDL (124 minute) and BCT-64HDL (64 minute) large cassettes. The camcorders and studio decks both accept the BCT-40HD and BCT-22HD mini cassettes (which run 40 and 22 minutes respectively).
The main advantages of selecting HDCAM over other formats, according to Robert Ott, Vice-President of VTR/Storage Marketing and Products is "that we've had an acquisition piece as well as a full studio VTR available for more than a year now. We have them in active use on major television shows such as Chicago Hope. It was the equipment that was used to produce the first high definition regularly scheduled program which was the Tonight Show. We've go a track record. Without a doubt, the HDCAM format, because it has had acquisition from day one, has made it a very viable format because it is not just an editing format such as telecine transfer or studio camera oriented; it's truly electronic field production and electronic cinematography. So, people are out there shooting in HDCAM right on their shoulder and that's a big advantage of this format. It is robust, it holds up just like the Betacam format which has a very good reputation. HDCAM has that same reputation for taking a beating and keeping on taping."
Sony is tight lipped about publishing details such as compression ratio, sampling frequencies, bandwidth, and the like. Sony will tell you that it uses DCT intraframe compression, but it's up to the user to do the math and conclude that it uses 7:1 compression.
Says Robert Ott, "We've been making ½" transports since 1982 in the form of Betacam, so basically, if we forget all the compression issues and everything that has to do with picture quality, if we just talk about someone taking a camcorder out and beating the heck out of it, for lack of a better term, we know we have products that take that kind of punishment and that's what the industry is looking for because they do beat the heck out of it. Not intentionally, but you know, they are on a rollercoaster, they are climbing mountains, they're doing everything with this equipment and they need a tape format that is a proven, reliable tape format. HDCAM, because it is based on ½" tape and we have so much experience in building transports, will take G-forces and everything else. HDCAM just lives off that legacy of ½". Basically, our philosophy is you can take a tape that was recorded in 1982 in a Betacam deck and play it back in a digital Betacam deck that was purchased last week. And that's the philosophy that we intend to follow through on all of our products."
The ATSC (Advanced Television Systems Committee) tables indicate that a 4:2:2 sampled 1080i image should have 1920 luminance pixels in the image. Chroma should be 960 pixels. Put another way, the 4:2:2 sampling should translate to 1920:960:960. Sony's HDCAM is said to record only 1440:480:480 pixels. If you do the math, this translates to 3:1:1, a number worse than 4:2:2. The numbers don't tell you everything, however; the HDCAM image is gorgeous and Sony challenges anyone to see the difference between the HDCAM output and that of its rivals.
The 3:1:1 numbers would also imply that the image is worse than a consumer DV camera (4:1:1) and this definitely not the case. A home DV camcorder has a sampling of 13.5 MHz yielding 720 pixels per line. According to the ATSC, HD is sampled at 74.25 MHz (true whether the format is 1080i, 1035i, or 720p) yielding 1920 pixels for luminance per line. Thus, 4:1:1 in the SD DV world means 720:180:180 pixels. In the HD world, 4:1:1 would mean 1920:480:480 pixels. So you can't compare DV's 4:1:1 with HDCAM's purported 3:1:1; that would be comparing grapes to grapefruit.
Now here's the real concern: HDCAM supposedly uses a 55.68 MHz sampling rate which should technically resolve to 1440 luminance and 480 chrominance pixels per channel. Comparing these numbers to the ATSC HD specs, we would come up with the number 3:1:1 which looks below par.
When pressed on the issue of how many pixels are being recorded by the HDCAM machines, Robert Ott could only state; "The HD SDI signal from an HD SDI standpoint, based on the SMPTE 292M standard, facilitates a 1920 x 1080 pixel baseband digital capability." The author conjectures that the VCR manufactures the missing pixels. Whether they're visually missed is a tough question. You remember (no doubt) from the sidebar earlier that if you have more data but compress it more, you hammer the picture sharpness.. Less initial data, compressed less, could look just as good.
The HDCAM is an eight bit machine, but Robert Ott goes on the explain, "HDCAM uses eight bit data reduction, but from a quantization standpoint, the inputs and outputs are ten bits. So, from a compression standpoint, we're eight bit data reduction. But from a quantization standpoint in the video, we're ten bits on the inputs and the outputs. "
Although Sony doesn't publish the number of bits being recorded on the tape (it's purported to be around 140 Mbs per second), Sony has interface boards that output whatever bit rates that are needed, such as 1.5 Gbps and 270Mbps SDTI.
Robert Ott was careful to point out that any rumors of Sony replacing its DCT compression with an MPEG-2 compression in the near future is totally false. Sony plans to support DCT compression in their HD line for the foreseeable future.
The author would not be surprised to see MPEG-2 rear its head in some HD product down the line. If you consider the Sony Betacam SX is MPEG-2 based at the standard definition 480i, it wouldn't be an outrageous leap to double the tape speed, add a little more compression, and go HD. The author would further conjecture that, at some time in the future, Sony would make a deck that played all their legacy formats besides (SX, digital Betacam, and HDCAM), since they all use the same sized tape.
Back to known facts, all HDCAM models will operate in both the 59.94 and 60 field per second modes.
HDCAMs have four editable 20 bit, uncompressed audio channels capable of 20 KHz frequency response. According to Robert Ott, "The 24p as well as the 1080i machine will be Dolby-E compatible which means that you will get eight channels. Two [of the format's 4] channels remain compressed, and the other two channels (When you record in Dolby-E, you are taking up two audio channels), can be converted to eight using Dolby-E. And the nice part about using Dolby-E is that all eight channels are still editable," unlike Dolby AC3 where once the signal is encoded it is no longer editable.
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