|adamwilt.com > the DV, DVCAM & DVCPRO Formats||copyright © 1998-2006 Adam J. Wilt|
|DV FAQ - technical||search|
|2006.07.16||-||Various updates throughout...|
|Detailed listing of this site's DV contents, and links to other sites.|
|The DV Formats Tabulated; standards documents & where to get them.|
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|DV formats, sampling, compression, audio, & 1394/FireWire/i.LINK.|
|linear & nonlinear; hard & soft codecs; transcoding; dual-stream NLE.|
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|DV sampling, artifacts, tape dropout, generation loss, codecs.|
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What is DV?DV is an international standard created by a consortium of 10 companies for a consumer digital video format. The companies involved were Matsushita Electric Industrial Corp (Panasonic), Sony Corp, Victor Corporation of Japan (JVC), Philips Electronics, N.V., Sanyo Electric Co. Ltd, Hitachi, Ltd., Sharp Corporation, Thompson Multimedia, Mitsubishi Electric Corporation, and Toshiba Corporation. Since then others have joined up; there are now over 60 companies in the DV consortium.
DV, originally known as DVC (Digital Video Cassette), uses a 1/4 inch (6.35mm) metal evaporate tape to record very high quality digital video. The video is sampled at the same rate as D-1, D-5, or Digital Betacam video -- 720 pixels per scanline -- although the color information is sampled at half the D-1 rate: 4:1:1 in 525-line (NTSC), and 4:2:0 in 625-line (PAL) formats. (See below for a discussion of color sampling.)
The sampled video is compressed using a Discrete Cosine Transform (DCT), the same sort of compression used in motion-JPEG. However, DV's DCT allows for more local optimization (of quantizing tables) within the frame than do JPEG compressors, allowing for higher quality at the nominal 5:1 compression factor than a JPEG frame would show. See Guy Bonneau's discussion of DV vs MJPEG compression for more details, or download the DVCAM Overview documents (PDFs) from http://www.sony.ca/dvcam/brochures.htm for a nice tutorial on compression.
DV uses intraframe compression: Each compressed frame depends entirely on itself, and not on any data from preceding or following frames. However, it also uses adaptive interfield compression; if the compressor detects little difference between the two interlaced fields of a frame, it will compress them together, freeing up some of the "bit budget" to allow for higher overall quality. In theory, this means that static areas of images will be more accurately represented than areas with a lot of motion; in practice, this can sometimes be observed as a slight degree of "blockiness" in the immediate vicinity of moving objects, as discussed below.
DV video information is carried in a nominal 25 megabit per second (Mbits/sec) data stream. Once you add in audio, subcode (including timecode), Insert and Track Information (ITI), and error correction, the total data stream comes to about 29 Mbits/sec or 3.6 MBytes/sec. Roger Jennings' papers run through the detailed numbers.
What's the difference between DV, DVCAM, and DVCPRO?Not a lot! The basic video encoding algorithm is the same between all three formats. The VTR sections of the US$16,500 DSR450 (DVCAM) or AJ-SDX900 (in DVCPRO25 mode) cameras will record no better an image than the VTR section of the cheapest DV consumer camcorder (please note: I am not saying that the camera section and lens of chead DV camcorder are the equals of the high-end pro and broadcast cameras: there are significant quality differences! But the video data recorded in all three formats is essentially identical, though there may be minor differences in the actual codec implementations). A summary of differences (and similarities) is tabled in Technical Details.
The consumer-oriented DV uses 10 micron tracks in SP recording mode. Sony's DVCAM professional format increases the track pitch to 15 microns (at the loss of recording time) to improve tape interchange and increase the robustness and reliability of insert editing. Panasonic's DVCPRO increases track pitch and width to 18 microns, and uses a metal particle tape for better durability. DVCPRO also adds a longitudinal analog audio cue track and a control track to improve editing performance and user-friendliness in linear editing operations.
Newer DV camcorders offer an LP mode to increase recording times, but the 6.7 micron tracks make tape interchange problematic on DV machines, and prevents LP tapes from being played in most DVCAM or DVCPRO VTRs.
Digital8?Sony's Digital8 uses DV compression atop the existing Video8/Hi8 technological base. Digital8 records on Video8 or Hi8 tapes, but these run at twice their normal speed (in the NTSC world; 1.5x in PAL land) and thus hold half the time listed on the label (2/3rds the time in PAL).
Digital8 also plays back existing Video8 and Hi8 tapes, even over 1394/i.Link/FireWire, allowing such tapes to be read into NLEs (at least, those for which the lack of timecode is not an issue -- batch capture utilities won't work, since Video8/Hi8 timecodes are not sent across the 1394 connection). Digital8 tapes themselves use the same timecode as DV.
Digital8 is largely a camcorder-only format, though two "Video Walkman" portable player/recorders are available. It appears to be the 8mm division's way of keeping its customer base from defecting to DV. By leveraging the massive investments of 15 years in 8mm analog camcorders and transports, the unit cost of Digital8 gear is kept very low, roughly half of what a comparable DV camcorder would cost, and its ability to play back legacy analog tapes is worthwhile for those with large libraries of 8mm.
Hitachi also produced Digital8 camcorders although these seem to be hard to come by (thanks to James M. DeLuca for bringing these "stealth" camcorders to my attention).
All Digital8 camcorders can record from the analog inputs (at least outside the EU), and all are equipped with i.Link ports for digital dubbing and NLE connections.
How good are the DV formats compared to other formats?DV formats are typically reckoned to be equal to or slightly better than Betacam SP and MII in terms of picture quality (however, DV holds up better over repeated play cycles, where BetaSP shows noticeable dropout). They are a notch below Digital-S and DVCPRO50, which are themselves a (largely imperceptible) notch below Digital Betacam, D-1, and D-5. They are quite a bit better than 3/4" U-matic, Hi8, and SVHS.
On a scale of 1 to 10, where 1 is just barely video and 10 is as good as it gets, I would arrogantly rate assorted formats as follows:
D-5 (10-bit uncompressed digital) 10 D-1 (8-bit uncompressed digital) 9.9 Digital Betacam, Ampex DCT 9.7 D-9 (Digital-S), DVCPRO50 9.6 DV, DVCAM, DVCPRO (D-7), Digital8 9 MII, Betacam SP 8.9 1" Type C 8.7 3/4" SP 6.5 3/4", Hi8, SVHS 5.5 Video 8, Betamax 4 VHS 3.5 EIAJ Type 1, Fisher-Price Pixelvision 1
[I had previously placed D-2 and D-3 uncompressed composite digital formats just below BetaSP, lower than any of the component formats. My feeling was that while D-2 and D-3 are excellent first-generation formats for composite analog playback and NTSC broadcast, the compositing of color with luma (which includes a color bandwidth limitation even more severe than DV or BetaSP employ) makes clean multigeneration and multi-layer image compositing problematic at best (even such simple things as adding titles).
However, I was severely upbraided by several folks with extensive digital composite experience, who all rated D-2 and D-3 between DV and DigiBeta. If you've got a high-end all-digital postproduction chain, the quality in these formats holds up over multiple generations extremely well, much better than any analog format, be it component or composite. While this is certainly true, if you don't have that all-digital pathway, I'm doubtful about how they would fare... so assume that D-2 and D-3 fall somewhere in the range between 1" and DigiBeta, and go have a look for yourself!
I've also moved 1" / BetaSP / DV formats down a bit numerically, though the relative rankings are preserved. Again, folks who live in high-end digital suites all day suggested this, and I have to agree. Bear in mind that my perceptions are largely predisposed to see BetaSP quality as pretty darned good; most of my work has been in analog component and Y/C editing with analog Y/C monitoring on PVM-series monitors. But after you sit in front of analog component or digital monitoring using BVM or Panasonic broadcast-grade monitors, your attitudes start to adjust upwards, and you start to discern differences between the merely very good stuff and the truly excellent stuff a bit more readily!]
Please note that I'm rating the formats here, not any particular implementation. For example, even though DVCAM and Digital8 are identical in their fundamental picture quality, a $16,500 DVCAM DSR450 is going to make a much better looking picture than an $800 Digital8 Handycam! Don't confuse the images produced by a bit of equipment with the underlying capability of its recording medium.
In resolution terms (at least in the 525/59.94, NTSC parts of the world), DV and Betacam SP can be compared as follows:
We'll assume the common rating of 80 TVL/ph (TV lines per picture height) per 1 MHz of bandwidth. Broadcast resolution is normally said to be 336 TVL/ph: 4.2 MHz luma bandwidth.
Sony rates BetaSP's luma frequency response to 4.5 MHz to the half-amplitude point, which works out to 360 lines. Oxide playback (i.e., Betacam, but not SP) is rated to 4 MHz (-6dB) which is around 320 lines.
By comparison, Panasonic rates DVCPRO25 at 5.75 MHz to the half-amplitude point, or roughly 460 lines. Other digital component formats are essentially identical [Yes, they're often said to be 500-line formats, but that's out to the point where amplitude response is down to 5%, or to the point where if you squint really hard you can imagine you can still see detail. By that measurement, BetaSP is probably good to around 400 TVL/ph or so!].
Chroma resolution on BetaSP is essentially the same as on 4:1:1 DV, so were BetaSP a digital format, its sampling might be characterized as 3:1:1 for comparison purposes. Of course, BetaSP is not sampled on a fixed spatial grid, so such numerical comparisions should always be taken with a grain of salt.
For a less biased discussion of DV quality, see the September 1998 SMPTE/EBU Task Force for Harmonized Standards for the Exchange of Program Material as Bitstreams Final Report, Annex C.
Jim Feely of DV Magazine used the Tektronix PQA200 Picture Quality Analyzer, a US$50,000 "black box" that calculates before/after picture differences and evaluates them based on Sarnoff Lab's JND analysis (a whole different topic -- in short, analysis based on modeling of the psychophysical characteristics of human vision), to evaluate a variety of formats for the May 1999 issue. I am hoping to get permission to repost that article on my site, as it's no longer available on DV's website nor in the Internet Archive.
What are the DV artifacts I keep hearing about?DV artifacts [Pix: Artifacts] come in three flavors: mosquito noise, quilting, and motion blocking. Other picture defects [Pix: Defects] encountered are dropouts and banding (a sign of tape damage or head clogging).
The most noticeable spatial artifact is mosquito noise around any sharp, contrasty edges. These are compression-induced errors usually seen around sharp-edged fine text, dense clusters of leaves, and the like; they show up as pixel noise within 8 pixels of the fine detail or edge causing them. The best place to look for them is in fine text superimposed on a non-black background. White on blue seems to show it off best. The magnitude of these errors and their location tends to be such that if you monitor the tape using a composite video connection, the artifacts will often be masked by dot-crawl and other composite artifacts.
A spatial quilting artifact can sometimes appear at the boundaries between 8x8 pixel blocks, most noticeable on shallow diagonals or on slightly-defocused backgrounds, typically when there is some motion in the scene to make the fixed "grid pattern" a bit more obvious. Some DV codecs seem to be much more prone to this than others, and with a few the quilting really starts to appear only after a few generations of rendering.
Motion blocking occurs when the two fields in a frame (or portions of the two fields) are too different for the DVC codec to compress them together. "Bit budget" must be expended on compressing them separately, and as a result some fine detail is lost, showing up as a slight blockiness or coarseness of the image when compared to the same scene with no motion. Motion blocking is best observed in a lockdown shot of a static scene through which objects are moving: in the immediate vicinity of the moving object (say, a car driving through the scene), some loss of detail may be seen. This loss of detail travels with the object, always bounded by DCT block boundaries. However, motion blur in the scene usually masks most of this artifact, making this sort of blocking almost impossible to see in most circumstances.
Finally, banding or striping of the image occurs when one head of the two on the scanner is clogged or otherwise unable to recover data. The image will show 10 horizontal bands (12 in PAL countries), with every other band showing a "live" picture and the alternate bands showing a freeze frame of a previous image or of no image at all (or, at least in the case of the JVC GR-DV1u, a black-and-white checkerboard, which the frame buffers appear to be initialized with). Most often this is due to a head clog, and cleaning the heads using a standard manufacturer's head cleaning tape is all that's required. It can also be caused by tape damage, or by a defective tape. If head cleaning and changing the tape used don't solve it, you may have a dead head or head preamp; service will be required.
This sort of banding dropout occurs fairly often; about once per DV tape in my experience. Usually it isn't even noticeable -- a single frame of banding due to a momentarily clogged head won't be visible unless there's motion in the scene to show off the frozen stripes. Have a look through your old tapes frame by frame (on a slow day, of course!) and you might be surprised how often you'll be able to find a single, subtly banded frame. For what it's worth, I've only rarely found such a banded frame on any DVCAM footage I've shot, which indicates to me that DV is right on the edge of reliability. DVCAM, with its 15 micron track width, or DVCPRO with its 18 micron track, are sufficiently on the safe side of the bleeding edge so that this sort of droput is much less likely to occur.
Bear in mind that analog BetaSP typically has several dropouts per minute; the last time I measured visible dropout rates on Hi8 and S-VHS I got numbers in the range of a dropout every 3-5 seconds (Hi8) and every 7-20 seconds (S-VHS). One visible dropout per hour-long tape, on average, is not something to get flustered about. But if it does bother you, shoot DVCAM or DVCPRO instead.
What are Digital-S and DVCPRO50?
JVC's D-9 (formerly known as Digital-S) and Panasonic's DVCPRO50 use two DV codecs in parallel. The tape data rate is doubled to 50 Mbps (video) and the compression work is split between the two codecs. The result is a 4:2:2 image compressed about 3.3:1. It's visually lossless and utterly gorgeous. Think of Digital Betacam, albeit at 8 bits instead of 10, at a bargain price.
JVC's D-9 uses the 1/2" SVHS form factor for tapes and VTRs, although the tape cassette itself is more robust and the transport is equipped with sapphire guide roller flanges and tape cleaner blades and a new scanner design. One of the D-9 players will also play back analog SVHS tapes, allowing its use for editing existing libraries of SVHS tapes as well as newer D-9 footage. Head life (so far, in on-air broadcast usage) is well in excess of 4000 hours; equipment cost is very low (comparable to 25 Mbps DVCAM or DVCPRO); and maintenance expenses are well below those of the Betacam decks that D-9 is typically displacing. Only JVC is supporting this format, which has resulted in a less-than-headlong rush by the video community to embrace it. Watch it, though; it's hot. If you're doing high-end EFP on a budget, this is the format to use.
Panasonic's DVCPRO50 uses the same DVCPRO tapes and transports as its 25 Mbps DVCPRO products (there is also a 93-minute DVCPRO50 tape, which Panasonic says should only be used in DVCPRO50 mode. When using standard DVCPRO tapes, the maximum recording time is about 61 minutes since the P123L cassette is being run twice as fast). DVCPRO50 VTRs will also play back DVCPRO tapes, and most will play DV and DVCAM tapes, too, though some of the decks cannot accommodate the miniDV cassette size, even using the cassette adaptor.
DVCPRO50 kit is real jack-of-all-trades stuff. Most of the camcorders record either DVCPRO (25Mbit/sec) or DVCPRO50 (50Mbit/sec) in either 4x3 or 16x9. One, the AJ-SDX900, can record in 24p (using either of the pulldown patterns used by the DV-format AG-DVX100A), 30P, or 60i at the flip of a switch.
Unlike D-9, second-sourcing is available from Philips, Hitachi, and Ikegami.
DVCPRO50 kit is also a lot more portable and lightweight than D-9, so it's the format of choice if you're doing high-end EFP with a somewhat bigger budget and you want to keep your camera operators from wearing out as quickly!
Panasonic also had DVCPRO-form-factor progressive-scan cameras and VTRs that use the 50 Mb/sec data rate to encode a 480-line proscan 16:9 image at 60 frames per second. DVCPRO-Progressive It looked very good -- but outlets for 480/60p media, ouside of the Fox network, are far and few between. People using 480/60p for digital filmmaking, for example, upconverted from 480p to 1080i HDTV, and sent the HD out to film. With the advent of the 480/24p-capable SDX900, as well as the 720p variable-frame-rate Varicam, Panasonic's DVCPRO-Progressive format has passed largely into history.
Four codecs for HD?
Both JVC and Panasonic showed working prototypes of 100 Mbps DV-derived products at NAB '99 for handling HDTV; Panasonic was shipping by NAB 2000. Both firms gang four DV codecs together to get the 100 Mbps datastream, while preserving the same equipment form factor and operational methodologies used in the current 50 Mbps products. Panasonic calls their stuff DVCPROHD, while JVC used the D-9HD moniker, reflecting the SMPTE standard number for their DV50 format. DVCPROHD is readily available, while D-9HD pretty much died on the vine and is not (as of 2004) a current product line.
In 1080/60i formats, DVCPROHD records 1280 Y samples and 640 Cr & Cb samples per line, compared to HDCAM's 1440 Y and 480 Cr & Cb samples. Thus the 1080-line DV100 formats have slightly lower luma resolution than HDCAM but slightly better chroma resolution (see the next section for a discussion of sampling).
1080/50i DVCPRO is said by certain uncorroborated documentation to be sampled at 1440x1080, and if still 4:2:2, that means there would be 720 Cr & Cb samples per line! I have not found a second source for this information, so I can't confirm it.
720p DVCPROHD records the 1280x720 image subsampled to 960 Y samples per line, maintaining 4:2:2 sampling to give it 480 Cr & Cb samples per line. 720p DVCPROHD always records 60 frames/second, but can, with the HDC-27 Varicam, record lower frame rates from the camera section by performing in-camera "pulldown", repeating frames as needed to record 60 per second. 24p, for example, is recorded with a standard 2:3 pulldown like the one described here, but with full frames instead of fields.
It should be noted that both Panasonic and JVC are well-placed to serve the growing DTV market whatever image format a broadcaster selects. Panasonic is selling switchable 720p/1080i D5-HD (not based on DV technology) and DVCPROHD VTRs. D5-HD has already become the studio standard VTR format for the dawn of US DTV. Some Panasonic camcorders, starting with the AG-HVX200, can record 480i, 480p, 720p, 1080i, and even 1080p (at 24 and 30fps), all using various DV/DVCPRO formats recorded on solid-state P2 cards.
JVC's NAB '98 and '99 displays featured D-9 variants of most popular ATSC DTV formats -- 480i, 480p/30, 480p/60, 720p, and 1080i, although the company seems to have pulled back from the DV-based HD market, instead focusing on an excellent series of 720p HDV camcorders and VTRs.
Sony's HDCAM format uses compression technology "derived from DV and with certain similarities", but it is not on the main branch of the DV family tree. Its data rate of 135 Mbps yields beautiful images; it's rare you'll see a noticeable artifact in an HDCAM picture.
What are 4:2:2, 4:1:1, and 4:2:0 anyway? [Pix: Sampling]These are all shorthand notations for different sampling structures for digital video. They are also used for CIF and QSIF and suchlike MPEG frame sizes, but in the discussion that follows, I focus on the numbers for SDTV (standard-definition TV) digitized to the ITU-R BT.601 standards: 13.5 MHz sample frequency and 720 pixels per line.
The first number refers to the 13.5 MHz sampling rate of the luma: "4" because (a) it's nominally almost approximately sort of four times the NTSC and/or PAL color subcarrier frequencies, and (b) because if it's "4" the other numbers can be integers whereas if it were "1" the formats would be "1:0.5:0.5", "1:0.25:0.25", and "1:0.5:0" respectively, and which would you rather try to read off in a hurry? The 13.5 MHz sampling yields 720 pixels per scanline in both 525/59.94 and 625/50 systems (NTSC and PAL/SECAM). This number applies to D-1, D-5, Digital Betacam, BetaSX, Digital-S, and all the DV formats just the same.
The other two numbers refer to the sampling rates of the color difference signals R-Y and B-Y (or, more properly in the digital domain, Cr and Cb)
In 4:2:2 systems (D-1, D-5, DigiBeta, BetaSX, Digital-S, DVCPRO50) the color is sampled at half the rate of the luma, with both color-difference samples co-sited (located at the same place) as the alternate luma samples. Thus you have 360 color samples (in each of Cr and Cb) per scanline.
In 4:1:1 systems (NTSC DV & DVCAM, DVCPRO) the color data are sampled half as frequently as in 4:2:2, resulting in 180 color samples per scanline. The Cr and Cb samples are considered to be co-sited with every fourth luma sample. Yes, this sounds horrible -- but it's still enough for a color bandwidth extending to around 1.5 MHz, about the same color bandwidth as Betacam SP (which, were it a digital format, would be characterized as 3:1:1).
So where does 4:2:0 (PAL DV, DVD, main-profile MPEG-2) fit in? 4 x Y, 2 x Cr, and 0 x Cb? Fortunately not! 4:2:0 is the non-intuitive notation for half-luma-rate sampling of color in both the horizontal and vertical dimensions. Chroma is sampled 360 times per line, but only on every other line of each field. The theory here is that by evenly subsampling chroma in both H and V dimensions, you get a better image than the seemingly unbalanced 4:1:1, where the vertical color resolution appears to be four times the horizontal color resolution. Alas, it ain't so: while 4:2:0 works well with PAL and SECAM color encoding and broadcasting, interlace already diminishes vertical resolution, and the heavy filtering needed to properly process 4:2:0 images causes noticeable losses; as a result, multigeneration work in 4:2:0 is much more subject to visible degradation than multigeneration work in 4:1:1.
"Now how much would you pay? But wait, there's more!" In US implementations of 4:2:0, the color samples are supposed to be vertically interleaved with luma, whereas in European 4:2:0 they're supposed to be co-sited. Practically speaking, this is a headache for developers of codecs, encoders, and DVEs, but for DV purposes it's not especially exciting, since only European DV is 4:2:0.
Why does PAL DV use 4:2:0?The best explanation I can come up with why PAL DV went with 4:2:0 is that both PAL and SECAM show reduced vertical color resolution and better horizontal color resolution compared to NTSC, so 4:2:0 seemed a closer match to the native display systems in PAL/SECAM countries. As PAL DV was intended as a consumer format for off-air recording or camcorder acquisition, multigeneration losses in 4:2:0 were considered a less important factor than the optimization of first-generation performance. PAL DVCAM also used 4:2:0.
When Panasonic developed DVCPRO, they opted for 4:1:1 even in PAL versions, specifically for the multigeneration advantage. Thus PAL DVCPRO decks have the pleasure and responsibility of handling both 4:1:1 DVCPRO playback and 4:2:0 DV playback; they have extra hardware to digitally resample the 4:2:0 signal and come up with a decently synthesized 4:1:1. Sometimes there is a reason for the higher prices that the poor Europeans are saddled with when it comes time to purchase gear...
Can I chroma-key with 4:1:1 / 4:2:0?Yes indeed. Many early DVEs were 4:1:1 internally; plenty of digital boxes out there still are (such as the Panasonic WJ-MX50 and Sony FXE-series vision mixers, both of which chroma-key). As previously mentioned, BetaSP could be considered a 3:1:1 format in terms of component bandwidth, and BetaSP is used for chroma-key applications all the time. With some care, DV25 keys at least as well as BetaSP; read on...
Part of the standard JVC sales pitch for D-9 is the superiority of 4:2:2 (which is true), and the utter doom and degradation that awaits you should you try to do anything -- including chroma-key -- with a 4:1:1 format (which is, shall we say, a wee bit exaggerated). But that doesn't mean that you can't do very satisfactory work in 4:1:1.
JVC had an excellent D-9 demo tape showing multigeneration performance comparisons of DV, D-9, and Digital Betacam; watch it if you can. Just be sure you take the hype with a grain of salt.
True, the chroma performance of 4:2:2 formats is superior to 4:1:1 formats, especially in multigeneration analog dubbing. But by the same token, 4:4:4 is as superior to 4:2:2 as 4:2:2 is to 4:1:1 or 4:2:0.
Where DV can get into trouble is that the coarse resolution of the chroma signal (only 180 samples per scanline in 4:1:1) leads to a very regular, "steppy" key signal, most noticeable on near-vertical edges or vertical edges where motion is present, especially if the codec's decompression simply replicates the chroma sample across the intervening pixels instead of low-pass filtering or interpolating between samples. The 4:2:0 sampling in 625 DV/DVCAM is somewhat better in this regard, but it has its own problems vertically, so there's always a tradeoff.
The single most important factor in good DV chroma-keying is low-pass filtering or interpolating the chroma prior to applying the keyer, so that the “steppy edges” are knocked off. Some codecs do a pretty good job of this by default (Avid DV); some can be set up for it (Matrox: Control Panel > Sounds and Multimedia > Hardware > Video Codecs > Properties > Matrox VFW Software Codecs > Settings... > Chroma Interpolation (YUV -> RGB)); with others you can add a filter (I have filters for FCP here).
Some people capture DV for chroma keying using an analog Y/C feed, since the analog connection prefilters and smooths the chroma.
The Matrox RTX.100 DV NLE board uses multi-tap resampling of DV's chroma to generate astoundingly good, crisp, finely-detailed keys in real time – so there is certainly enough information on DV's chroma for most keying purposes; the only tricky bit is recovering it intelligently!
Additionally, use the matte choker and/or matte feathering and smoothing controls of your keyer to round off the edges a hard-cut key signal gives you. I've had excellent results with After Effects Production Bundle's Color Difference key, and superb results also using the Chroma Keyer in Final Cut Pro 3. Using these tools I can make very clean and acceptable keys, certainly for hard-edged keying. Spill supressors (or “edge enhance” in FCP 3's Chroma Keyer) are essential in cleaning up any remaining chroma spill in the foreground video.
You may also find that layering different key signals gives you excellent results. I've used a heavily-choked chroma key to cut my main matte, but then add one or two luma, extract, or difference keys to define the edge detail that the chroma key can't get. Each luma key may only work for a small part of the image; it may lose the greenscreen background but also lose the interior of a similarly-bright face. However, it usually is able to get edge detail, because the edges of a person fall off in shadow or are picked out brightly by the rimlight, and the chroma key holds the interior matte that the luma key won't provide.
DV-aware keyers like dvGarage's DV Matte Pro (for After Effects or Final Cut Pro) do a great job of keying DV; if you're frustrated by the standard software keyers provided with your NLE or effects package, try an add-on keyer. I used to struggle with FCP's chroma key, even with my add-on chroma smoothing filter (or the ones Apple supplied starting in FCP 4.0), but DV Matte Pro is so much better (and easier to use) I almost can't compare it. I simply kick myself for not trying it out sooner!
John Jackman has some good examples of DV keying on his post-production pages at greatdv.com.
Can I use 4:1:1 / 4:2:0 DV sources for upconversion to HDTV?
All SDTV source material will suffer when upconverted to HDTV, compared with material originated in HD to begin with. 4:1:1 and 4:2:0 material is reported by some to be problematic in this aspect; certainly a 4:2:2 original will be more forgiving and if upconversion is your primary goal, you may want to look closely at D-9 (Digital-S) or DVCPRO50.
Snell & Wilcox have run DV through upconversion and reports that it look OK, especially if the excessive aperture correction (edge enhancement) in most DV cameras is turned down.
Of more concern is that DV artifacts, especially mosquito noise, may become annoyingly prominent when upconverted. However, the jury is still out on this; I've performed upconversions without excessive artifacts, but a lot depends on the subject material. Again, reducing edge enhancement helps.
Also, HD material is 16:9. The way many DV cameras produce 16:9 by throwing away vertical resolution is enough to send shudders up my spine for SDTV work; for HD, it'll be a complete disaster. Perhaps I should add a section on shooting for HD upconversion; there are lots of issues...
What is 1394 and/or "FireWire"?IEEE-1394 is a standard communications protocol for high-speed, short-distance data transfer. It has been developed from Apple Computer's original "FireWire" proposal (FireWire is a trademark of Apple Computer). Check out the 1394 Trade Association, white papers on Adaptec's website, and DVCentral's links for pointers to additional 1394 sites for detailed information.
Sony calls their implementation of 1394 "i.LINK".
Why are DV and 1394 always discussed together?They appear to have been developed together. The data stored on DV tape appear to reflect the packet structure sent across a 1394 link to a frightening degree of exactness. Certainly the DV format and 1394 High Performance Data Bus co-evolved, such that the first consumer DV camcorder in the USA (the Sony DCR-VX1000 and its single-chip brother the VX700) was also the first 1394-equipped consumer product available.
What does a 1394 connection do for me?Plenty of good things:Some time ago I edited a friend's wedding, going from Hi8 camera originals to a DV edit master. The 20-minute ceremony was covered by two cameras; we sync-rolled the VTRs and mixed the show in real time as if it were live. At the end, we weren't sure we liked it. So we dubbed it off via 1394 to another DV cassette, inserted a fresh DV cassette, and had another bash at the edit. This time, we liked it. We put the tape into the VX1000 and set up the DHR-1000 VTR as the recorder, using the built-in editor to drop the second attempt in frame-accurately atop the first across the 1394 wire. No generation loss. And we still had the first edit on the backup tape, should we have changed our minds.
You can make digital dubs between two camcorders or VTRs using 1394 I/O, and the copy will be identical to the original. You can do cuts-only linear editing over 1394, with no generation loss. You can stick a 1394 board into your computer (PC or Mac), and transfer DV to and from your hard disk. If your system can support 3.6 MBytes/sec sustained data rate -- simple enough with many A/V rated SCSI-2 drives and with most ATA/EIDE drives these days -- the world of computer-based nonlinear editing is open to you without paying the quality price of heavy JPEG compression and its associated artifacts, or the monetary price of buying heavy-duty NLE hardware and banks of RAID-striped hard drives.
Is 1394 that much better than Y/C or component analog?Yes. A 1394 dub is a digital copy. It's identical to the original. That's really nice.
Yes, you can do almost the same thing with a SMPTE 259M SDI (serial digital interface) transfer. But VTRs with SDI cost big money. 1394 is built into many low-end cameras and VTRs, and the connecting cable -- even at Sony prices -- is only US$50; you can find it for US$20 if you shop around.
Also, transferring via 1394 is a digital copy, a data dump (as it is over the expensive SDTI interface on high-end DVCAM and DVCPRO VTRs). No decompression or recompression occurs. Transferring DV around as baseband video, even digitally over SDI, subjects it to the small but definite degradation of repeated decompression/recompression.
If a digitally-perfect copy is a 10, and a point-the-camera-at-the-screen-and-pray transfer is a 1, here's how DV picture quality holds up over different transfer methods:
IEEE-1394, SDTI 10 SDI 9.8 Analog Component (Y, R-Y, B-Y) 9 Y/C ("S-video") 8 Analog Composite 5 Point camera at screen and pray 1
What's the deal with DVCPRO gear and 1394?DVCPRO, or D-7, is a DV-based format with a few subtle differences in its datastream. These changes were made by Panasonic's engineers to improve the robustness and reliability of the DVCPRO system when compared to DV, but they do mean that certain data header bits do not conform to Blue Book standards. Thus a direct data interchange between DVCPRO gear and DV/DVCAM gear is not possible in the same way that DV and DVCAM gear can interchange data; furthermore some nonlinear editor systems are not capable of accepting or generating a DVCPRO-compatible signal.
As a result, DVCPRO gear with 1394 connections can only exchange data with other DVCPRO systems, not with DV or DVCAM gear. Since a 1394 transfer is a direct data dump, this is understandable; if a cross-format transfer were to be possible it would require that one deck or the other "translate" the signal to or from the DVCPRO data format to the Blue Book format.
As far as incompatibility with 1394 transfers to and from NLEs, this limitation is expected to diminish (and eventually vanish) as developers get a chance to work with DVCPRO over 1394, and to provide switches inside their programs to supply a Blue Book or DVCPRO datastream as required. Matrox, Canopus, and Apple, for example, have DVCPRO compatible NLEs.
Remember, DVCPRO was designed first and foremost as an ENG format; robustness of the signal was paramount, and interconnection of gear in the ENG world is done via analog or via SDI (1394 is too limited an interface for the broadcast world, where the ability to switch and route video over thousand-meter runs is both necessary and taken for granted; 1394 has a length limit of 4.5 meters and requires a point-to-point session-level communication instead of a switchable open-ended transmission). 1394 was added to the DVCPRO lineup as an afterthought, at the prompting of customers, and as it becomes more prevalent (and if the marketplace demands it) you'll see more NLEs capable of dealing with DVCPRO data as readily as with Blue Book data, and possibly even realtime DV/DVCPRO format translators.
What's the difference between locked and unlocked audio?Locked audio is "audio done right": the audio sample clock (the digital time reference used in the sampling process) is precisely locked to the video sample clock such that there is exactly the same number of audio samples recorded per "audio frame" of video (not all TV formats and sound sample rates have a neat integer relationship between audio samples and frames, so an "audio frame" is my term [similar to a "color frame"] for the number of video frames it takes for audio and video to match up in the same phase relationship).
For PAL, 625/50 video, locked audio provides exactly the same number of samples per video frame with either 32 or 48kHz audio, but for NTSC, 525/59.94 video, the 48kHz "audio frame" is 5 video frames: locked audio will provide exactly the same number of audio samples for every five video frames, though not every frame within that 5-frame sequence has an equal number of audio samples. 32kHz locked "audio frames" cover a whopping 15 video frames!.
[There is such a thing as an AES/EBU audio frame, but I'm not sure it that's the same thing I'm referring to. Comments/clarifications welcomed!]
Unlocked audio: theory:Unfortunately, such precisely-locked audio clocks are expensive. Since DV was designed as a consumer format, unlocked audio was allowed as a cost-saving measure. In unlocked audio, the audio clock is allowed some imprecision, such that there can be a variation from the locked spec of up to +/- 25 audio samples written to tape for every frame, instead of a precise and exact number.
This economy measure is simply one of allowing the audio clock to "hunt" a bit around the desired frequency; the phase-locked loop (or other slaving method) used to keep the audio sampling in sync with the video sampling can have a bit more slop in its lock-up, with the audio sampling sometimes running a bit slower, sometimes a bit faster, but always staying in sync over the long run. The total amount of sync slippage allowed in unlocked audio is +/- 1/3 frame -- not enough to really worry about.
It's the difference between walking a dog on a short leather leash, always forcing the dog to stay right by your side (locked audio), and using a long, elastic leash or one of those "retractable clothesline" leashes that allows the dog to run ahead a bit or lag behind (unlocked audio). In either case both you and the dog will get where you're going at the same time, but along the way the "unlocked" dog has a bit more freedom to deviate from your exact walking pace.
Unlocked audio should not cause audio sync to drift away from video over a long period of time. The audio clock is still linked to the video clock; it's just allowed a bit more oscillation about the desired frequency (more wow & flutter if you will) as it's trying to track the video clock. Like the dog on the springy leash, it can run a bit ahead or a bit behind the video clock momentarily (up to 1/3 frame ahead or behind), but in the long run it'll still be pacing the video clock and on average will be right there in sync with it. I have shot one-hour continuous takes of talking heads with a consumer DV camcorder (DCR-VX1000) and experienced no drift at all between audio and video.
DV cameras and VTRs generate unlocked audio, both in 32 kHz 12 bit and in 48 kHz 16 bit recordings. DVCAM and DVCPRO cameras and VTRs generate locked audio in 48/16 audio format, and DVCAM can also generated locked 32/12 audio. 44.1kHz, discussed below, is never locked; it has no neat integer relationship with either 625/50 or 525/59.54 frame rates.
Some non-linear DV/1394 editors generate locked audio, some output unlocked, and some allow the choice. Final Cut Pro through version 1.2.1 (at least) generates locked audio always, but it doesn't set the flag to tell the VTR that it's locked -- so the VTR reports it as unlocked.
DV gear is happy to record locked audio via 1394, just as the DVCAM DSR-20 VTR will accept unlocked audio. The DVCAM DSR-30 VTR and DSR-200 camcordercan also be made to record unlocked audio with a bit of coaxing (see Video Tidbits).
Also, many non-linear editors output 16 bit 44.1 kHz audio (at least on PC platforms), which both DV and DVCAM 1394-equipped decks record without any problems. 44.1 kHz is part of the Blue Book spec, so this is not too surprising.
(Many thanks to Earl Jamgochian at Sony for filling in and clarifying many of the details in this section.)
Unlocked audio: real life:"The difference between theory and real life is that in theory, there is no difference between theory and real life, but in real life, there is a difference." -DV Filmmaker Marshall SpightWhile the theory sounds good, real life is sometimes a bit different. Some manufacturers appear to take the word "unlocked" literally; a completely separate clock seems to be used for the digitization of audio, with no direct linkage or locking to the video clock. The result is an audio timebase stability that's excellent (since no "hunting" around a target frequency is present), but the possibility arises of a long-term drift between audio and video, when processed independent of each other.
This was revealed at NAB '99 by Randy Ubillos, lead engineer on Final Cut Pro, who has found that while most DV cameras are pretty good, Canon cameras grab 48kHz sound at around 48.009 kHz, which can result in almost a second of video/audio slippage over the course of an hour (or around one frame every two minutes). Sonys, by contrast, seem to average 48.001 or 48.0005 kHz, resulting in perhaps a couple of frames of slippage over the same time period (and I haven't seen any slippage in my own tests of the VX1000). Clocking rates for other cameras were not discussed.
In normal playback of the DV tape this isn't seen, since on playback the audio is played back based on its embedded clocking data, in sync with the image. Both the audio and video slave to the data samples in each packet; as these are commingled in the DV datastream, the sound and picture will always play back in sync. It's worth saying again: when playing a DV tape, audio never drifts, regardless of whether it's locked or unlocked.
Final Cut Pro allows captures limited only by available disk space, and the QuickTime media format used treats audio and video as separate tracks, each with its own time reference. When capturing long unlocked-audio clips, drift can become apparent; Final Cut can measure this drift and recalculate the audio sample frequency so that QuickTime playback will stay in sync (the AutoSyncCompensator or Sync Adjust setting, depending on your version of FCP)..
Canopus NLE products allow a similar recalculation; they have special .ini file flags for dealing with Canons (check the notes following the table for "Compatible Hardware: DV Cameras and Decks" in the support section at http://www.justedit.com) . Other NLEs have their own ways of dealing with the problem -- or not, depending on the NLE.
As more NLEs adopt Type 1 AVI files for DV storage, another aspect is becoming clear. Like the audio on a DV tape, Type 1 files have their audio and video intermingled in the DV stream, so no drift ever occurs. And now that the dreaded 2 Gig limit is mostly a thing of the past, people are capturing entire tapes to disk in one pass. So far, so good. But many of the tools people want to use (like some DVD authoring programs) still want Type 2 AVI or QuickTime files; and audio drift can occur when one exports a long program from Type 1 to Type 2 or QuickTime. Over the course of an entire, hour-long tape, even minor inaccuracies in the unlocked audio clock can lead to noticeable sync slippage or drift.
Typically, one doesn't discover this until the last minute, of course: when converting the files to Type 2 for use in DVD or web authoring. For this reason I suggest that if you use a DV product with unlocked audio, and any part of your production toolkit requires Type 2 AVI or QuickTime files, that you capture and edit in Type 2 or QuickTime using an NLE that understands how to reclock the audio as described above.
Will unlocked audio hurt me? How do I deal with it?When using analog audio I/O, the whole question of locked vs unlocked is moot: it's analog and there are no clocks to worry about. Analog is always safe to use for dubbing or editing. As discussed above, DV audio data are converted to analog in real time as the data come off the tape, and audio slippage simply doesn't occur regardless of the accuracy of the sampling clock.
It should also be of no concern when taking the audio in via 1394 to a DV-based nonlinear editing system. When all the audio samples are stored in a neat memory array, the software doesn't care if there was some timebase instability on the original recording; when non-real-time rendering is occurring, a sample is a sample is a sample.
However, some long-term slippage between audio and video can occur in long clips, at least in QuickTime and Type 2 AVI formats, if the capture application doesn't compensate for any audio clock inaccuracy.
Fortunately, the problem is understood by those in the business (at least at Apple, Canopus, and Digital Origin), and corrective measures are taken at capture time: Final Cut Pro measures the actual number of samples captured over time vs. the theoretical number, calculates the actual effective sampling rate, and uses that in QuickTime file processing.
As discussed in the previous section, though, captures in Type 1 AVI format that are then converted to Type 2 or to QuickTime may show slippage or sync problems with unlocked audio. At this point (late 2001), I strongly suggest sticking entirely to Type 1 AVIs, OR entirely to Type 2 AVI / Quicktime files throughout your production and post-production workflow.
Unlocked is a potential problem when doing real-time audio and video editing with digital transfer of the audio between source and recorder. "Digital" means conveyance of the audio using the IEEE-1394 bus, AES/EBU digital audio outputs (on pro DVCAM/DVCPRO VTRs), or SDI embedded audio (ditto).
As far as DV-based editing is concerned, when you make an edit in the digital domain between two different DV datastreams using unlocked audio, you might wind up with a few too many audio samples or not quite enough, in which case you can get a click or pop on the soundtrack during playback as the audio subsystem either has to discard some extra data and resynchronize (an audio buffer overrun), or as it winds up with too few bits of sound to cover the time available (buffer underrun) and you get a momentary dead spot or mute effect (depending on the audio circuitry used, the system may also mute when it's resynchronizing after discarding samples). In either case the audio glitch will occur in a fraction of a second; it won't result in several seconds of dead audio or any prolonged audio noise. Reportedly, it's also only a problem at the out-points of insert edits, not at edit in-points (unverified).
Interestingly enough the same problem may occur when cutting between two locked audio streams without regard to synchronization of the "audio frames", though here the problem is much smaller in scope since the variation in sample counts will only be +/- 2 samples per video frame. Such errors are typically inaudible, though they may still complicate things if the audio track is then used in real-time digital audio mixing (see below), and they'll only occur in 525/59.94 video, never 625/50 due to 625's 1:1 relationship between video frames and "audio frames".
[It's also worth noting that any hard cut between clips can result in a pop or click if the instantaneous level of the audio at the cut point is mismatched, causing impulse noise. This is true in locked or unlocked audio; it can even occur when working in analog. This is one reason that linear analog audiotape and film fullcoat mag tracks are often spliced at an angle instead of with a straight cut; this mechanically performs a quick crossfade between the two tracks instead of an abrupt transition.]
When all you are doing is editing one generation down from camera originals to an edit master, and then making release copies on an analog format such as BetaSP, SVHS, Hi8, VHS, or the like, all you need to be concerned about is audible popping or muting. The release copies will contain an analog track that records what you hear; there are no hidden gremlins due to asynchronous clocking, jitter, or other nasties that so complicate digital audio.
However, when you take the digital audio datastream from a DV tape and try to integrate it into a larger digital audio system, such as AES/EBU routers, digital audio workstations (DAWs), and/or multitrack digital audio recorders including the Alesis ADAT and Tascam DA-88/98, the sloppy synchronization of unlocked audio can cause glitches, artifacts, and distortion. If the receiving gear is trying to derive its audio clock from the unlocked audio datastream, the entire downstream audio chain can be rendered unstable and disfunctional.
Furthermore, playback of unlocked audio including edit-point glitches as discussed above into a DAW or other digital audio system can cause a major commotion when the edit-point glitch is played back. Ever had a really bad splice go through the gate on a film projector, or past the heads on an analog audiotape recorder? A glitched unlocked audio edit is the digital equivalent of that crummy splice, only worse!
Fortunately it's fairly simple to avoid this. Either convert unlocked audio to locked, or use analog audio connections between your unlocked source and the digital audio chain you're feeding (and if your source tape has 44.1kHz/16 bit or 32kHz/12-bit sound, going analog into the digital system means that you get a rate conversion into 48kHz sound at however many bits are being used courtesy of the A/D converter on the professional digital system; it may actually sound better -- and be easier -- than hooking up digital sample rate converters in the chain).
There are five known ways to convert unlocked audio to locked audio:
1) Many high-end DVCAM VTRs convert unlocked audio to locked audio on playback. DVCPRO VTRs are also supposed to relock DV audio on playback. This solves your problem at the point of playback. If you need to make a tape with locked audio, then...
2) Dub your DV tape to a DVCAM or DVCPRO tape using analog audio connections between the source and the recorder. Hey presto, locked audio! The video can be dubbed via SDI for minimal if any losses. This is also the recommended route of your source audio is not 48kHz since you want the dub to have 48kHz audio for best compatibility.
3) Play back the DV tape in a high-end DVCAM or DVCPRO VTR, and dub it to a high-end DVCAM or DVCPRO VTR using either the AES/EBU digital audio or the SDI embedded audio options. The player will reclock the data and the recorder will write locked audio to tape. Some of the top-end decks even relock audio on the 1394 connections; check the deck's documentation for this feature.
4) Transfer your footage into a non-linear editor that allows outputting locked audio, and use the NLE to write out locked audio, even to a DV-format tape. Slow and cranky, but it works.
5) Audio guru Jay Rose says, “There's another way to lock an unlocked: a number of current pro audio devices will accept blackburst as their sync reference, and reclock incoming AES/EBU streams to match. I've been doing it this way in my Orban DAW for years.”
How do I intermix locked and unlocked audio?It's best not to intermix any variations of digital audio on the same tape. While VTRs seem to cope with sudden changes in sampling rate, bit depth, and locked/unlocked status, often you'll get a brief moment of silence at the transition between audio types as the internal workings of the audio chain readjust themselves to the new audio type. Some non-linear editors are very uppity about audio changes; if you start digitizing a 48 kHz clip and the audio changes to 32 kHz, you'll get silence for the entire 32 kHz section (or vice versa; once the capture card and software start grabbing data at a certain rate, they're too busy to try to change rates in mid-stream. Furthermore, the meta-data stored with the clip can only remember one audio format per clip). And if you try to digitally feed such mixed-mode tapes' audio into further digital processing, major glitches can be expected.
The best thing when doing a linear edit is to use analog audio, or (if the only changes you have are between locked and unlocked audio) use the digital outputs from a high-end VTR as described above. For non-linear editing, capture clips each containing only a single format of audio; when you render the finished project, all the audio will be converted to a common format.
Does unlocked audio explain why my audio loses sync in Adobe Premiere (or Final Cut Pro, or...)?Well, yes and no. Adobe Premiere 4.2 and earlier versions had a historical problem with synchronous audio playback from the timeline. Premiere 4.2 audio can drift regardless of whether the source was locked or unlocked. This particular problem is variously attributed to the difference between 30 Hz and the 29.97 Hz that NTSC runs at; the inability of an AVI or QuickTime file to maintain synchronous audio; the weakness of the Windows VFW subsystem at really keeping things in sync, and the phases of the moon (if anyone knows what's really going on, this author would appreciate being appropriately enlightened).
Premiere 5.1 fixed 4.2's audio sync problems. Certainly I had no problems with Premiere 5.1 on Windows editing clips up to 9:30 in length (the 2 Gig limit of that early AVI-based system), nor have I heard of any such problems in discussions with other people.
If, however, you're capturing longer takes, or entire tapes, to disk in one pass, you can run into unlocked audio sync drift over the length of the clip.
If you find you're getting sync slippage, check two things, especially on QuickTime-based editors: (1) when you capture a clip, make sure that the sample rate selected in the capture menus is the same as the sample rate on tape, and (2) set your timeline/sequence options to use the same sample rate as your captured clips (reportedly, not doing this is causes sync drift in Final Cut Pro). It also can't hurt to make sure your video capture settings are correctly set to 29.97 fps (NTSC) or 25 fps (PAL).
If you're shooting with a Canon camera and editing Final Cut Pro, make sure you've enabled AutoSyncCompensator or Sync Adjust (if your version of FCP has those options; they became permanenty enabled in FCP 4 or later). Likewise when using certain Canopus NLEs, make sure you've set the proper Canon flags in the .ini file. Canons (more than most) have unlocked audio drift problems; see above.
If you're capturing long clips in Type 1 AVI file format, and then exporting to Type 2 or Quicktime, you might see sync drift after the export that wasn't apparent in the original capture. Solutions: either capture tapes scene-by-scene instead of all at once, or switch your capture and editing system to use Type 2 or QuickTime instead of Type 1.
Does DV support line 21 Closed Captioning (EIA-608-A)?DV supports NTSC analog Closed Captioning (CC) on line 21 (EIA-608-A). It's part of the spec. DV, DVCAM, DVCPRO, and Digital8 all have the capability to handle CC, as they are all derived from the same spec.
Which DV devices support Closed Captioning?Not all decks or DV-to-analog converter boxes handle CC properly (note: even decks and camcorders that don't properly support CC data will properly transfer it over FireWire. “Proper support” in this context means encoding the analog CC into DV data and decoding it back to analog).
Jeff Schriebman, who wrote CCaption and MacCaption, says:
The SONY decks such as the DSR-11, 20, 25, 30, 40, etc. handle CC correctly. The high end Panasonic [DVCPRO] decks do, too. I haven't checked the low end ones. All SONY Digital8 Camcorders that I have checked do CC properly. The SONY PD-150 does, the Canon XL1 doesn't.Jeff says that Digital8 camcorders from Sony process CC properly, and that's what he recommends for folks looking for a cheap DV-to-analog or analog-to-DV converter that processes CC data correctly.
The now defunct SONY DVMC-DA2 converter box handled CC correctly. None of any of the other FireWire to analog boxes that are currently on the market [as of October 2003] do CC correctly including the Promax. The AJA/Apple interface combination does not handle CC properly either.
I can add that the DHR-1000 DV deck also handles CC correctly. The LSI/C-Cube DV codec supports closed captioning; this hardware codec is used in video servers from Omneon (Spectrum) and Avid / Pinnacle (Thunder) as well as many hardware-assisted DV NLEs.
While the DSR-80 handles CC, the DSR-85 does not, according to Bill Eastham at Mt. San Antonio College in Walnut, CA:
We have braved our way through many layers of support at Sony, most of their support people told us that it should work, but when we challenged them to duplicate our efforts, they finally admitted that the 85 does not do captions. They also said that there should be a menu setting, but when they got into the machine, they couldn't find it either.Apparently CC got squeezed out of this special-purpose deck, which earns its keep performing 4x realtime SDTI transfers.
I have reports that JVC cameras and decks don't process CC data, and that JVC service personnel have told customers that DV doesn't support captioning!
What about DTV Captioning?EIA-708-A, ATSC DTV captioning, post-dates the creation of the DV spec. To date there are no DV codecs (to my knowledge) that handle ATSC captioning other than embedded 608-compatible line 21 captions.
Why doesn't DV seem to have any 7.5 IRE setup?[A quick note to PAL users and non-North-American NTSC users: North American analog video has its black level raised about 7.5% from the zero-voltage black level used elsewhere in the world. This "pedestal" or "setup" is what's being discussed.]
Native DV, like any properly-recorded digital component format, doesn't have setup. Setup exists only in the analog world and has no relationship to DV as an encoding scheme or as a tape format. DV looks like it has setup (or not) because the decks that DV is recorded in / played from may add setup (or not).
All 601-conforming digital formats record nominal black at a luma level of 16, and nominal white at a luma level of 235 (in a 0-255 range, using 8 bits: there are 10-bit versions, too, like D-5 and DigiBeta, where the range is 64-940, but the DV formats are all 8-bit formats so we'll stick with 16-235 for this discussion).
When played over FireWire or over SDI or over SDTI, that's what you get: blacks at 16, and whites at 235. When you interchange files digitally, whether as DV-format stream files or QuickTime or AVI with the appropriate DV codec, black is 16 and white is 235. The same numbers hold, by the way, if your computer file holds 601-format uncompressed data, or DVCPRO50 data, or HDCAM, or DVCPROHD, as long as it's stored as "YUV" (really YCrCb) and not transcoded to RGB (wherein a whole range of gain/offset problems can occur, and even a gamma change if you're using Final Cut Pro; see white clip for some of the gory details).
Now, when you play back to analog, what happens? Digital levels get converted to analog levels, and that's where setup enters the picture (or not).
In Europe and Asia, analog video's blacks are at zero voltage: 0mV PAL, 0 IRE NTSC. In North America we add a slight offset, the infamous 7.5 IRE of setup, for historical reasons (the DC regulation of early sets was poor, and electron beam retrace suppression didn't exist, thus the designers provided a safety margin between "black" and "blanking" levels so that retrace wouldn't be visible even if the viewer's TV set was slightly misadjusted).
Going from analog to digital and back again, if you're following the spec, analog black goes to digital black and vice versa. Whether digitizing from NHK in Tokyo (0 IRE setup) or NBC in New York (7.5 IRE setup), the black levels in the digital data should be the same: 16. Likewise, the blackest black in a picture coming out of the camera section of a camcorder should always be laid to tape with a luma level of 16, regardless of what part of the world the camera is designed for. And that same tape should play back in Japan with 0 IRE setup, and in the USA with 7.5 IRE setup.
What makes this magic setup level change? There's no flag in the data -- there doesn't need to be. "Bits is bits," after all. The simple answer is that Japanese digital decks add no setup, and American decks add 7.5 IRE of setup.
Huh? Remember, I said "at NBC." NBC and their partners in crime will be using proper, broadcast/professional NTSC DVCPRO and DVCAM decks. Such decks have, buried in their menus, the option to "add setup". In Japan and Korea, that setting is properly turned off. In the USA, that setting should be on. By the same token the better camcorders offer "add setup" switches in their menus for their analog outputs.
A similar setting removes setup on incoming analog signals; it should be on in the new world, off in the exotic east.
Now, the Rest of Us may be using lower end gear: DSR-20s, DSR-11s, PD150s, even consumer gear. None of these low-end decks and camcorders have "add setup."
So if you take a tape shot in a DV or DVCAM camcorder and play it back in one of these low-end decks, the analog output will NOT have setup. The playback will be fine in Asia, but it'll be "too dark" in the Americas.
However, the tape itself, and the recorded data on it, are absolutely and completely conformant to the 601 spec, because setup simply doesn't exist in the digital domain! The same tape plays back setupless in a DSR-11, but with setup on a DSR-2000 or AJ-D455 with "add setup" turned on.
But remember that that's only a parameter for the analog outputs! If you connect any of these decks to an NLE over 1394, they will all play back an identical image into the NLE, no matter how the switch is set. By the same token playing back (from the high-end decks) to an SDI monitor will always show a correct black at the same level no matter how you set the "add setup" switch.
Are all digital formats like DV in this regard?Yep. The difference is that only DV and DVCAM have such low-end gear available, so that a lack of added setup on the analog I/Os can cause us such grief. DigiBeta, DVCPRO, and D-5 users never see this issue because all their equipment properly handles setup.
How's this handled in analog broadcast?Those guys use a deck that properly adds setup to analog outputs and strips it from analog inputs. Or they use a cheapo deck and use a proc amp to add/remove setup.
If an NLE handles everything DV native all the way, it's not US NTSC legal, right?Sure it is. If I haven't lost you yet, you'll have twigged to the fact that digital, as long as it's digital, ain't got no setup nohow, nowhere, no way. DV, DVCAM, DVCPRO, DigiBeta, D-5, you name it. Whether it's FAST.blue, Sony XPRI, FCP, or Avid (XpressDV or Symphony), when it comes to setup, "I've got plenty of nothing, and nothing's plenty for me." If you've got analog I/O built in on your NLE, that I/O may or may not have setup. Most do, or can be configured for it (see below for the details using DigiSuite).
If you're using a DSR-30 or 40 or a Canon GL1 or other low-end DV/DVCAM device as your analog I/O, no, you haven't got setup on the analog outs, because those machines don't add setup.
I have a DigiSuite (or similar NLE with both digital and analog I/O). If I go in and out of the NLE with DV material using SDI or 1394 I'm fine, but if I go into the NLE using SDI or 1394 and out using analog to BetaSP, I have no setup. What's wrong?The fact that SDI and FireWire I/O is OK means that the digital levels inside the NLE are correct. The unsetup analog means that no setup is being added on the analog outputs. It's possible that the system was installed with "NTSC (Japan)" selected, in which case no setup will be added no matter what, or that the 7.5 IRE option is turned off. I'll discuss the DigiSuite DTV in detail, because I'm familiar with it, but the same general concepts apply to other NLEs as well, so you might want to keep reading and look for similar configuration options in your system of choice.
With DigiSuite DTV running DigiUtils 7.0, fire up the DigiSuite Control Panel, select "Video Out", and look at the Video Level Adjustments. If you've got "Broadcast" or "Post-production" selected, setup will be added (click the "Settings" button to check), but if you've selected "DV compliant" then setup will NOT be added. That's fine (and correct) if you're recording the analog signal on a low-end DV or DVCAM deck, but wrong if you're going to a deck that expects to see setup. If you want to keep the "DV compliant" superwhite rendering option, but add setup, select "Custom" and choose "Allow Super White Only" for Luminance Range and "7.5 IRE" for Analog Setup.
If you can't select 7.5 IRE, and you ARE running the DigiSuite in NTSC, then either the system registry has been corrupted or the DigiSuite was installed for setup-free "NTSC (Japan)". In either case uninstalling and reinstalling DigiUtils is the way to fix it.
Other hardware-based NLEs will have other options; consult the online help, the installation manual, and the operations manual for details on your system.
Can I deal with the problem by adding setup at the capture stage so that the analog output would be correct? Is a digital signal with setup applied wrong?It's wrongwrongwrongwrongwrong! Did I mention it was wrong?
You won't have any file interchange with other NLE users. Your black levels will be about 8% too high in the digital data. Any still frame you export will have washed out blacks. Any tape you makes via SDI, SDTI, or 1394 will have washed out blacks. This error will require annoying rendering (software) or a global tweaking of the realtime proc amp hardware to correct. And in either case, you've lost precision in your digital data, which only makes luma banding and other quantization errors more visible.
My pedestal needs defining.Define it by recording bars at the head of your tapes that encode the proper black level. That way when the operator at the dupe house or the station puts your show up on the scopes she'll see whatever level the blacks are at and tweak her proc amps appropriately. It doesn't hurt to label the cassette with a setup-level warning, too.
I've made downloadable single frames of DV/DVCAM, DVCPRO, and DVCPRO50/D-9 colorbars. They're generated using the superb, linear, and spot-on accurate Matrox software codec and stored as generic AVIs, so they should be usable directly in any NLE using AVI or QuickTime files with a DV codec (with the possible exception of Canopus, which may not be able to read the "dvsd" data correctly).
Some DV and DVCAM camcorders like the AG-DVX100, DSR-PD150, DSR-250 can record a video signal with "7.5% setup." Is that OK?The AG-DVX100, PD150 and DSR-250 have a "7.5% setup" setting in the menu. Don't use it! It does not add setup to the analog outputs; it modifies the digital data coming from the camera head by boosting the black level, resulting in washed-out blacks, reduced precision, and nonstandard tapes as described above. As a result the analog video played back from the camcorder or viewed live has its blacks at 7.5 IRE, so the signal looks like it has setup, but what it really has is a too-high black level!
The "7.5% setup" setting in these cams are really only useful if you're:
- using the camcorder as a camera only, in switched multicam shoots where the other cameras have setup;
- intercutting camera footage with off-air signals recorded on a deck like the DHR-1000 that similarly does not remove setup on analog inputs, thereby creating washed-out-black footage;
- intercutting camera footage in an NLE with images brought in via analog dubs to DV tapes or live E-E digitizing when such A/D is done using low-end decks/camcorders that do not properly remove setup from incoming analog signals.
In these last two cases be aware that you're essentially working in your own little nonstandard "island" of washed-out-black digital data, and that intercutting with properly-digitized material won't be possible without (a) black level shifts or (b) lots of annoying rendering using the levels filter.
Do not confuse these cheap imitation "7.5% setup" controls with the genuine, pukka article as present on DSR-300s and 500s and the like. Those "add setup" controls in "Real" cameras are proper analog setup tweakers that do not screw up the digital data.
As far as I know no DVCPRO cams/decks suffer from these problems because they all have proper setup adding/removing options in their menus or on their switch panels.
I don't know what the story is with Panasonic's "DV Proline" cameras like the AG-DCV15 and AG-DVC200, or the AG-DV1000 and AGDV2000 VTRs. My guess is that the DV200 has proper "add setup" controls, but that the others may not. Similarly I'm not familar enough with JVC's "ProDV" and "CineLine" DV kit to say for certain how they're equipped in this regard.
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