Advantages Of DVD How a DVD Works DVD Construction DVD Design Considerations
DVD Storage Archiving Vs Editing Links to DVD D-Mystified® & DVD FAQ DVD Player Compatibility
Released in the US in 1997, the DVD had somewhat of a rocky start. It was complicated by a number of competing interests. Movie companies wanted iron clad copy proof protections, while consumers wanted to be able to use it for personal recording - unencumbered by copy restrictions for their own personal use. Whatever was agreed on, the manufacturers had to be able to produce it for cheap if it were to be affordable. Out of the convoluted mess evolved the Content Scrambling System, parental protection schemes, region encoding as well as others. The DVD as we know it today is the end result of many compromises between the competing interests. You could almost say the format succeeded in spite of the bloody battles. Initially, simple DVD players like you find now at Wal-Mart selling for $39 or so, initially cost about $1,000.
Initially all DVD consumer equipment were players only, but by the year 2000, the first consumer recordable's started to appear. Pioneer initially sold their first DVD-R recorder for a paltry $17,000. ($17,000 is NOT a misprint !) Amazingly, they sold like hot cakes since previously, the only other solutions out in the market were commercial burners that sold for about $150,000 ! $17 Grand was an absolute steal !
DVD burners probably had one of the fastest and greatest price reductions in recorded history. Prices fell faster than the companies that purchased the first ones released could ever hope to depreciate them for tax purposes. As of Sept 2005 Wal-Mart sells a basic DVD recorder for $98.97 ! That's less than 1/1500th the initial cost in under 6 years ! Recordable DVD media has also plummeted from about $15 to $20 to about 36 cents each for good quality media.
Why DVD ? ....... DVD offers numerous advantages over magnetic tape.
First of all, they make for GREAT table leg adjusters and beer coasters !
Videotape typically has a life expectancy of from only 10 to 20 years depending upon many variable factors. Though still the best medium to originate in, conversely, it's the poorest medium to archive in, due to it's relatively short life. (Read more....)
Unlike videotape, the DVD disk is never in contact with rotating heads, head drums, capstans, pinch rollers, guide posts, bearings, audio heads or control track heads.... All of which the tape must "grind" over each time it is played. There is no mechanical wear to a DVD disk, since it is scanned solely by a low power laser beam.
The disk is also not susceptible to magnetic fields, serious chemical breakdown or the damaging effects of hydrolysis as is videotape. Nor are they susceptible to being "eaten" by an errant VCR.
Once recorded, DVD-R and +R media cannot be recorded over by accident.
The DVD disk is digitally recorded. Thus the the 1,000th time you view it will be just as clear as the very first and copies of the discs will be perfect digital clones !
Plus the estimated life based on manufacturer's testing of a DVD is between 30 and 100 years ! Being Digital, the image will be just as sharp & clear over the life of the DVD as when it was created ! (Compare that to 10 - 20 yrs for a videotape - even if never played and stored in a controlled environment).
Even so, 80 years isn't forever....... But that solution is already in the works so to speak !
Future emerging technologies will inevitably employ digital formats as well. When those emerging technologies appear, the digital data from the DVD can be simply exported to the new medium and format, the end result being that video converted to DVD today can be virtually timeless..... Something handed down from generation to generation !
It's almost mind boggling to think that in 500 years or more, your offspring could be watching how great great great great great (etc etc etc ) grandma and gramps appeared in family videos as kids growing up way back in the 1980's - before the turn of the millennium even !!! The digital data will be transferred onto the new mediums and formats - all without losses ! Thus, the video they'll watch in the year 2503 will be just as sharp and as clear as when your DVD was mastered ! Only until the advent of digital DVD has it become economically (not to mention technologically) feasible !
A great digital conversion is now taking place across the entire world. Museums and archive libraries are scanning in priceless artwork to DVD before it is lost. Sadly, many films & photo prints were lost over the past 100 years. With the advent of Digital technology, those works are now being preserved.
Family histories and family trees are being saved to CD and DVD. Two years ago I scanned all our family pictures in. Some were even on tin plates - burned them to CD, and sent CD's to each of my cousins. The concern of those pictures ever being lost or destroyed by fire for example is no longer a fear.
Videotapes from the 60's & 70's are now being preserved as well. A lot has been lost, as some of the 2" quadruplex tapes received are incapable of being played anymore. The thrill of getting one back never grows old and is hard to describe !
Most firms that "push" DVD transfers, forget to mention that DVD's do have some disadvantages that are worth considering.......
They occasionally make for GREAT table leg adjusters and beer coasters ! (like when things don't go EXACTLY as planned...))
The digital files are in compressed MPEG-2 format. To achieve that wonderful compact file size so that 2 hrs of reasonably high quality video will fit on a DVD, something has to "give". Most noticeable are the resulting motion artifacts and naturally some loss of fine detail as compared to uncompressed analog component or much less compressed digital formats. Even so, the image quality far surpasses standard VHS or even S-VHS for that matter and artifacting in the XP 1 hr mode that uses the least compression, is barely noticeable even if you're looking for it. Even burning in SP mode which allows up to 2 hours to be placed on a single layer DVD, artifacting is not that that evident unless you "go looking" for it. DVD's burned in 4 or 6 hour modes using the highest levels of compression is a different story, where artifacting is much more pronounced.
We're often asked why we don't recommend editing from a DVD. It's not that you can't do it, it's just that doing so has limitations using some lower end editing software. To fully explain it would take many pages, turning this topic more in to an engineering/technical paper. Rather than bore anyone to tears (including myself) this is the highly condensed explanation as simply as I can figure to write it !
If you plan to edit the video at a later date, then DVD would not be my first choice. Better and more stable results are obtained from video recorded to tape formats such as DVCAM, MiniDV, BetaCam-SP, DigiBeta or even S-VHS for that matter. It all has to do with MPEG-2 compression. First and foremost, DVD's are all MPEG-2 compressed. Like audio, uncompressed avi files for example will yield cleaner video than any MPEG compressed file, as there's simply more visual information with which to work. Although XP and SP burned DVD's don't suffer much of a penalty as far as image quality is concerned, there are some other issues that come about from trying to edit MPEG-2 compressed video.
Part of how MPEG-2 achieves such high compression ratios while still maintaining high image quality, owes to the concept of generating reference or information frames every so often and then generating intermediate frames that define only what has changed between frames. A lot of "bits" can be saved by not having to repeat an unchanging background over and over again ! To accomplish that, DVD Video Discs are comprised of i (information), P (predicted) and B (bi-directional) frames. i frames are somewhat similar to a jpeg image in that the entire original frame is compressed - background and all. As such, i frames serve as the starting reference for the intermediate P & B frames. You can think of the P & B frames on the other hand, as storing only the image changes (Blocks in motion) between the I frames. Thus i frames tend to be large while P & B frames that store only the image changes, tend to be much smaller. Since there tend to be many more P or B frames generated than i frames, compression ratios of 21 to 36 are common. On average, there will be only 2 i frames generated for every second of video. Two i frames per second is not a cast in concrete number, as the actual number of generated I frames can vary depending on the MPEG encoder and how much information changes from frame to frame. But for the purposes of trying to understand the concept, figure on two i frames per second as being the norm.
It's easy to see that editing I frame to I frame poses no problem, but trying to make a match edit between any other frame combination will often result in something of less than admirable results - since at the edit point, the I frame references will have abruptly changed to the new material. In case it still isn't all that "easy to see" I'll try and explain this another way...... A typical sequence of MPEG-2 frames for example, would be I BB P BB P BB P BB P BB I BB P BB P BB P BB P BB I BB P BB P BB etc etc etc . Make an arbitrary edit somewhere in the middle, & chances are you'll have broken the normal sequence. A "B" frame for example now might not have the correct preceding i frame that contains the proper background info. If left uncorrected, the decoder in the player will "hiccup" at the break in sequence and the resulting frame content at the edit point can be somewhat unpredictable. The severity will vary between almost transparent to an outright glitch depending on the inter-frame motion, how drastic the image changes & how far out of sequence the frame sequence logically got. Some software is "smarter" and will attempt to generate new i frames to keep a logical sequence if it can come rendering time, but many packages won't even bother to try.... Most folks won't notice the "hit", since with typical "slash n' hack" editing, there was a drastic image change at the edit point anyway and our brains won't "notice", since it takes several milliseconds to process the new visual information. Precise match frame editing however is a different story & will result in a noticeable glitch or jump that will stick out like a "sore thumb" at the edit point... Most consumers do pretty simple cut and paste editing and rarely if ever do much in the way of match frame or multi-layered builds. So for them it is far less of a concern.
Some of he better software packages will get around those problems created by breaking of the i,p,b sequence, by regenerating new i frames and restoring the proper sequence. It does pose a penalty in terms of increased rendering times, but makes for clean edits.
So yes.... you can edit MPEG-2 video, but it might have some limitations depending on how sophisticated your editing software is.
Finally, though DVD's are far more resilient & durable than tape, they are not indestructible. Their small size makes them easy to drop, and a serious scratch or gouge near the hub where often the critical INF and BUP files are written, can render the disc unplayable. Also, their nice compact size and light weight makes them easy to drop, where they are then easily stepped on or be subjected to being driven over by the wheels of an office chair....... (CRUNCH..... bye bye DVD !!! )
Note also that the Azo, Cyanine, Phthalocyanine or Oxonol dyes used in DVD±R media are subject to fade if exposed to direct sunlight or other UV sources and the damage is accumulative. Like any polycarbonate plastic, subjecting them to high heat or any solvent will have instant devastating consequences.
The DVD (Digital Versatile Disc) was developed in 1993 by the Toshiba Corporation. While DVD optical discs are quite similar in many ways to CD-ROM optical discs, there are several physical differences. The CD-ROM was originally designed to accommodate high quality audio as well as text based data data. The format worked so well that it has been expanded to include video data as well. CD's however are not well suited for the storing of broadcast quality video and due to their 650 MB limitation, cannot contain anywhere's near a full length movie at high quality. The DVD however, excels in the inherent weaknesses of the CD technology.
CD to DVD Comparison & Specifications
|Disc Diameter||120 mm||120 mm|
|Disc Thickness||1.2 mm||1.2 mm|
|Disc Structure||Single Substrate||Two Bonded 0.6 mm Substrates|
|Laser Wavelengths||780 nm (infrared)||650 and 635 nm (red)|
|Track Pitch||1.6 microns||0.74 microns|
|Shortest Pit Length||0.83 microns||0.4 microns|
|Pit Groove Depth||.16 microns|
|Data Capacity||650 Mbytes||4.7 – 17.0 GB
(4.7= single layer single side
17GB = double layer double sided)
|User Data Rate||1.4 Mbits/sec||10.0 Mbits/sec|
The physical dimensions of both media types are exactly the same, but the differences end there. Note that the DVD track pitch is less than half the spacing and the shortest pit length is also less that half that of a CD. In able to achieve this much higher density, the DVD uses a red laser beam as opposed to an infrared beam on the CD. The shorter wavelength of the red laser allows a much smaller focused beam width. Future designs soon to come are the "Blue Ray" laser with a much shorter wavelength that will allow much greater data densities.
The much narrower red laser beam of the DVD explains why a DVD player can easily read a low density CD, but a CD player cannot read the narrow tracks or higher densities of the DVD.
The DVD is capable of being manufactured with 2 layers as opposed to only a single layer as found on the CD. Double layering allows twice the capacity per side and is found on commercial DVD's usually offering bonus features and director's cuts.
Single Side - Single Layer (DVD-5)
This is by far the most common and least expensive DVD. This format holds 4.7 GB of data (or about 7 times the amount of a CD). Using MPEG-2 compression, this allows approximately 2 hours of high quality video with embedded audio to be recorded. The format is referred to as DVD-5 (the 5 representing the rounded off digital data capacity in gigabytes)
Single Side - Double Layer (DVD-9)
This construction holds approximately 8.5 GB. The second layer is below the semi-transparent layer of the top or first layer. The laser beam merely has to re-focus on the more distant bottom layer to resolve the data stream. Since all the data is on two layers on the same side, it is not necessary to flip the disk over. The DVD-9 allows extended play time and is sometimes used to record "Director's Cut's" or extra "bonus" footage on a single DVD in addition to enhanced audio such as DTS Surround sound.
Double Side - Single Layer ( DVD-10)
This DVD construction holds up to 9.4 GB and are commonly used to put a widescreen version of a movie on one side, and a full frame version of the same movie on the other side. Access to the "B" side requires flipping the DVD over as only a few players will accomplish this automatically.
Double Layer - Double Side (DVD-18)
The highest capacity DVD construction that can hold up to 17 GB (about 26 times the data capacity of a CD) - or about 8 hours of video. It's really just a double sided version of the DVD-9. Owing to the high costs of producing this format, their use is very rare.
Note that in this illustration the laser beam as in your dvd burner, comes in from the bottom which is the recordable side
The DVD-R is manufactured from a clear layer of polycarbonate plastic which provides a stable base and gives the DVD physical strength. Above the polycarbonate base is a thin layer of laser sensitive dye (usually a dark green) and atop that, a thin reflective layer that reflects the laser beam back to the read head. Next is added a protective lacquer coating to which a hard polymer based coat is added to guard against scratches.
Writing data to the DVD is done by a red laser beam modulated by the serial data stream. When the beam turns "on" and hits the dye layer, a distortion (known as a pit) on the surface is made. Though it's often referred to as "burning", no actual burning or melting of any sort is done in the typical sense, though it does rapidly heat the dye with an 8 to 10 milliwatt beam. Just sounds more impressive to "burn" a DVD instead of "tanning" one with a laser beam so the terminology stuck.... ! The color and composition of the dye layer is designed for maximum absorption of the red laser wavelength, thus allowing inexpensive and safe, low power laser devices to be used. When the beam "burns" a distortion, it's referred to as a "pit" though some circles refer to it as a "stripe"
Reading the data back is done by a much lower power laser setting (one that will not "burn" more unwanted pits) that serves as a coherent tightly focused light source for the detector.
Three objectives had to be resolved to make the DVD a financially viable medium.
First:....... The linear velocity of a DVD must be held constant and be able to reproduce a vertical frame rate of 29.97 frames/second to meet RS-170A specifications for sync signals to maintain compatibility with the rest of the video world (at least in the case of creating a Video DVD). Consider that if the rpm is held constant, then the linear velocity will be quite different from the inner tracks compared to the outer tracks. Thus there must be a mechanism to measure the linear velocity and accurately adjust the disk rpm to maintain a constant linear velocity.
Second: ....... Every DVD player had to have absolute tracking accuracy to insure the extremely narrow laser beam would scan exactly in the middle of the track where the data was recorded. Consider that the track width on a DVD is only .74 um (microns) in width - which is much smaller than a single hair which is typically 50 microns in diameter. Approximately 67 DVD data tracks would fit rather nicely in the width of a single human hair ! Add to that, the vagaries of rotating mechanical hardware, fluctuating power line voltages etc, and it became obvious this was not going to be an easy inexpensive task if conventional design approaches were taken.
Third: ....... The real engineering "killer" was that the DVD player had to be made affordable (read: Cheap !) if it ever was to be a viable product. Building sophisticated tracking electro-mechanical mechanisms into each DVD player and have them remain compatible with high repeatable accuracy across different manufacturer's product lines and media offerings, was not an option. No way that was ever gonna work at an even semi - reasonable price tag. Add to that the mechanism being jostled about in shipping etc, and it was a real engineering challenge. So some clever engineers dreamt up a system whereby each "blank" DVD was to have what is known as pre-grooves. Thus a blank DVD disk isn't really blank at all. The disk already is pressed with the track grooves accurately pre-cut and encoded with a constant bit rate frequency.
There are notable differences between DVD-R and +R formatsDVD-R
The pre-grooves in the case of DVD-R and DVD-RW discs, are not perfect spirals. Instead, the groove is modulated with a constant frequency of 140.6 kHz, known also as the wobble frequency (since the groove actually wobbles !) Much like a lateral cut phonograph groove, groove wobbling means that the grooves wander back and forth in sinusoidal fashion at a fixed amplitude. This constant frequency allows accurate tracking by the laser as well as provides a highly accurate timing signal to which the write clock frequency is derived.
Between the grooves are the pre-pits. The pre-pits contain the sector addressing information so the servo control knows what part of the disc is being scanned and where to find specific content.
The +R format pre-groove also uses a wobble frequency, but at a much higher frequency of 817 kHz. Instead of pre-pits, the +R formats convey the sector addressing information by frequency modulation of the wobble frequency.
Thus the + and - format DVD's are quite different in their approach to encoding sector addressing and other low level information, although physically they look the same visually to us.
There are a wealth of technical articles on the web delving into the differences in much greater detail, but this is the simple gist of it all !
Anyways, these pre-grooves solve the two most perplexing problems. First of all, the position of the tracks are now accurately controlled at the time of DVD manufacture, allowing a simple and inexpensive linear tracking mechanism to be used in the player/recorder. All the DVD player now has to do, is to read the constant frequency in the pre-groves and keep the signal peaked...... a simple task. The frequency of the recorded "tone" also provides highly accurate timing pulses which are used as an accurate timing reference.
Thus much of the impressive accuracy required to make the system work was done when the "blank" DVD was pressed.
Newer DVD technology, employs a blue laser with a much shorter wavelength. Data recording densities employing the blue laser will offer up to 27 GB on a single layer side - that's greater than 5 times the capacity of a standard DVD !
Also added is the DL (Double layer) recordable media and DL capable burners - allowing up to approximately 8.5gb per side. So far the DL recordable technology is limited to the +R format. Prices for blank DL media is still a bit "steep", but will undoubtedly drop as the efficiencies of mass production increase.
Manufacturer and independent testing labs estimate the life of a DVD anywhere from 30 to 100 years if properly stored & handled. Exactly how accurate (or overly optimistic) these estimates are, won't be confirmed for another 30 to 100 years. Torture testing includes temperature and humidity extremes to get a handle on how long the media will last, but a lot of unpredictable factors such as exposure to airborne pollutants aren't taken into consideration. Thus we tend to lean much closer to the 30 year estimate.
In another even 25 years or so, the real issue won't be whether the DVD will have survived, but rather will be the problem of trying to find a working DVD player with which to make the transfer to whatever new format is in vogue... It's another case where the media will outlive the availability of equipment upon which to play it. Technology is moving at an ever faster pace and the video field is already awash in over 70 dead, abandoned or obsolete formats. Though the standard 4.7 Gb DVD is prevalent today, it will quickly become obsolete with the introduction of new technology if history is any lesson.
Regardless of how long the DVD will reign, we naturally want to achieve the greatest longevity of the medium..
To achieve the manufacturer's full estimated lifespan requires a certain amount of care. Though regarded as a resilient & durable archival medium, they are NOT indestructible.
Above all, avoid direct exposure to direct sunlight or any Ultra-violet source. Failure to heed this advice is guaranteed to result in an "early retirement" of the DVD. The ultraviolet radiation will fade the dyes as well as cause breakdown of the polymers. Just as severe, any adhesive labels will deteriorate resulting in separation and subsequent imbalance of the disc. Naturally ink jet color labels will also fade. Inkjet labels on good stock are fine if applied with a precision applicator, but care must be taken to keep the DVD and it's affixed label out of any prolonged exposure to sunlight or other ultraviolet source (which includes fluorescent lighting).
Avoid "bargain" media like the plague..... High quality media doesn't cost all that much more than low grade
The DVD-R must have been recorded on a suitable working DVD writer, with proper calibrated laser power levels (most newer writers are quite accurate). There are slight differences between media manufacturers in the formulations of the dyes used however. Note that just because brand X media worked great in one of your DVD burners, that brand may cause nothing but headaches in another model burner even though it was a high quality brand. Thus most DVD burner manufacturers will note on their web site, brands that have shown to yield excellent data integrity for that model.
The surface should contain no scratches or fingerprints. Though resilient, the oils and acids present in our hands has a detrimental effect on polycarbonate over time. Always handle a DVD by the outer edges - never by the hub (Data is recorded from the center hub to the outside, and the critical INF and BUP files are often on the inner most tracks). Manage to cleverly destroy the INF & BUP files and the DVD is "history".
Media should be stored in a jewel or DVD case in a temperature controlled environment. Archival storage calls for temps in the range of 39 to 73 deg F and 40 to 50% RH. Exposure to excessive heat (ie: above 158 deg f) will destroy a DVD. (Yet another reason not to leave a DVD exposed to direct sunlight or stored in a hot attic)
Exposure to acids or solvents will spell instant disaster.
Make 2 copies of your most valuable DVD's. One copy to be played and the other to be stored always in a safe dark place.
Be sure to mark the DVD with the format (ie DVD-R, +R , -R/W +R/W etc). In another 50 years or so, your grandchildren won't have even heard of a DVD. The transfer houses of the future that transfer vintage DVD's will want to know exactly what your descendents have and the format of the recorded material. Simply marking the DVD now will solve that problem.
Though DVD's offer numerous advantages as explained above, video which is to be edited later is best saved on a digital format tape. The video recorded on all DVD's is recorded as highly compressed MPEG-2 data. This allows typically 1 to 2 hours of high quality video to be transferred to a single DVD or up to 4 or 6 hours of lower quality video. Compressed MPEG-2 however, does not always lend itself to the best end quality should the video be desired to be edited in the future. Transferring to digital formats such as DV, MiniDV, Digital8, DVCAM, or Digi-Beta yields the best results in this case, as the digital video recorded on tape is only lightly compressed employing a lossless 5:1 ratio technique. Other options are to store the digital stream as binary avi files on computer archive/backup tapes such as DLT, 3490, 3490E,H etc.
Though the tapes be they digital video or computer tapes, have a short life as compared to DVD, transferring the data is lossless, and the tapes may be refreshed as many times as desired.
Confused by all this ???
Just give us a call and we'll explain it in better detail.
There are expensive high quality DVD's and there are the inexpensive brands or "no brand". The quality control on the bargain media often ranges from poor to non-existent. You may "luck out" and get a good batch, or more times than not, you won't be so lucky. Often times the cheap media sold is what's known as "B" or "C" stock. Those are the discs that failed to meet the rigid quality standards of reputable manufacturers and are then sold off to merchandisers who sell them for cheap. Other manufacturers simply make low quality media by "cutting some corners" to gain market penetration via a lower price point. Often times, the cheap media often results in burning many a beer coaster or another to be added to your already vast collection of table leg adjusters. In just about all cases, "bargain" media is no bargain in the end.
Although a DVD may look like a simple piece of cheap plastic, it has to be manufactured to extremely rigid and critical physical standards.
So how do I tell which is the best media to use ?
Well, it depends on your burner. Many manufacturer's sites have recommendations as to which media have been found to be compatible with their burner. But in general, there are some "brands" to be avoided like the plague. www.digitalfaq.com has an informative page dedicated to this common question. It's worth reading before rushing out and purchasing a large quantity of DVD recordable's.
You may also want to download the DVD Info software, which will usually identify the actual manufacturer of even the no-brand discs. The routine also has a surface sector check routine to map out any surface defects. Detail and additional links to download sites, may be found at the web address below.
There are numerous reasons for this common malady, but what follows are the most common.
1. Cheap warped media or media warped due to exposure to heat
The tolerances of DVD's are very tight and the slightest distortion of the disc can result in the servo system not being able to keep up with the high speed wobbling of the disc. DVD's are written beginning at the hub and work their way out towards the edge. Any warpage of the DVD usually results in severe wobble towards the outside edge. The symptom is that the first 30 min to an hour will play back fine, but the last 30 min to an hour or so will exhibit skipping or freezing. The problem will become even more noticeable towards the end of the disc where the wobble is much more pronounced. Other discs due to sloppy manufacturing, may also be unbalanced or the spindle hole may be stamped slightly off center, also inducing a wobble and varying time base. Remember that 67 tracks will easily fit in the width of a human hair. It takes very little distortion of the disc to cause problems and will not be detected by a simple cursory visual inspection.
2. Dirty laser lens
Over time, the laser lens will become dirty. We simply live in a "dirty" world - there's no avoiding it other than building a certified clean room. Contaminants from wood/Coal burning stoves, forced hot air heating systems as well as proximity to the kitchen where grease laden air is common, can quickly build up a film on the laser lens. A DVD player that was once working flawlessly, will start to exhibit skipping, freezing and artifacting problems. Lens cleaners and CD/DVD cleaning kits sold at places such as Radio Shack® make the cleaning task easy. A simple cleaning of the laser lens will often breathe new life into your player/recorder. Many a DVD player has ended up in the local landfill, simply because the lens was dirty.
3. Dirty Media
DVD's, owing to their high track & data densities, are more prone to dust and grime than are CD's. Even so, they are quite tolerant of light dust etc on playback. Note: use of the word "tolerant" is not meant to imply that a DVD that looks like it just got fished out of a dumpster is ok ! ......... The media must be reasonably clean to effect reliable playback.
In sharp contrast however, they are NOT nearly as forgiving of the tiniest amount of contamination when burning. Anything that blocks or attenuates the laser beam from altering the dye layer during the burning phase, will usually spell disaster or variations thereof ! Be sure to keep media sealed until use and check for any dust before inserting into the recorder. Inexpensive media has often been re-packaged & exposed to non clean room environments . Many come "pre- filthed" !
Even though a DVD is tolerant of some fingerprints and dust on playback , the oils & acids present in fingerprints can wreak havoc with the polycarbonate over extended periods of time.
4. DVD±R CompatibilityStandard Commercial DVD's are pressed and literally stamped out at the rate of 700 or more per hour. DVD±R's are instead "burned" one at a time on stand alone DVD-R burners whereby a dye layer is "burned" by a small low power laser. Thus a DVD-R is constructed quite differently than a commercial stamped DVD.
A DVD-R will have a dark greenish - Blue appearance on the recording side, which is the dye layer. A stamped DVD has no dye layer and will appear shiny. Thus a DVD-R has a much lower reflectivity than does a standard DVD. To enable reliable playback, a DVD-R capable player has an additional laser pickup, optimized for the lower reflectivity of a DVD-R. If a non DVD-R capable player has a DVD-R placed in it, the outcome can be unpredictable. A few DVD's may actually play ok, or more likely, will either skip - freeze or be unpredictable in operation. Most won't play at all.... Even though one DVD-R may play ok, the next may not. A DVD-R that once played ok, may not play the next time..... This is due to the sensor operating right on the edge of readability.
The best way to know if the DVD player supports DVD-R, is to read the owners manual. If it does support DVD-R, it will almost always clearly say so. If it makes no mention of DVD-R, then you can safely assume it does not support DVD-R, as it is a major selling point and is always well advertised & marketed ! Note: (The same applies for DVD+R and ±R/W)
Note: commercially pressed DVD's are more resilient than the burned dye based DVD's we burn in our CD/DVD drives... So why even bother with burned dye based media ? It's all about cost. Pressing DVD's are done at a rate of about 800 per hour. It lends itself to high speed mass production. The problem is the cost... To make the master pressing costs on the order of $3,000 due to the complexity and specialized equipment which is neither small nor cheap.... Then add to that a 1,000 disc minimum order. The cost to make just one DVD would be at least $4,000 to $5,000. The cost of making the master can be amortized easily when making 10,000 copies, but impossible to amortize over making just one DVD. Compare that to burning one where a good burner now can be had for less than $70 and the blank burning media costs on the order of around 30 CENTS each.. Dye based DVD's are not the best technology, but they are the most cost effective by far and the only optical recording technology that is affordable to the consumer market..
5. Burning Speed
Although your burner may support 2x, 4x or even 8x burn speeds, the media itself may not - or vice versa. There is a fine balance between the dye layer formulation, response to the laser, laser power levels and speed of the burn. They are all inter-related.
It's somewhat akin to passing your finger thru the flame of a candle. A quick pass thru, and you'll barely feel it if at all.... Stop and hover your finger over the flame however, and you'll end up with a charred finger (assuming your central nervous system is functioning properly and you can stand the pain).
Burning a DVD isn't conceptually much different. Upset that delicate balance between burn speed, laser power and dye layer formulation, then skips & freezes will be the likely result. Rule of thumb: When in doubt, burn at a slower speed.
Modern burners have built in microcode that contains the "Write Strategy" for the media. Write Strategy is just a fancy name for a lookup table the DVD burner uses to set laser power levels for the type and brand of media inserted. With write strategies becoming more refined, modern burners are compatible with far more media brands, though there is still room for improvement.
6. Dye Fading
Relatively short exposure to ultra violet as found in direct sunlight, can fade the dyes within as little as a few days. Even indirect florescent lighting can can begin to fade the dyes given enough time. To prove it to yourself, burn several test DVD's and leave in a window exposed to direct sunlight for several weeks with a pencil or something else covering part of the recordable surface. Won't be long before you'll see the where the now faded dye has left an outline around the object. I can guarantee you that the DVD given enough fading will eventually become unplayable.
7. DVD Labels
Off center labels can also cause an unbalanced situation resulting in skips and freezes. If you print your own adhesive labels, DO NOT attempt to apply the labels by hand, even if you have a steady hand & "good eye" for such things. Use a label applicator which will perfectly align and center the label each time. Even the best media will skip & freeze if the label is even the slightest bit off center.
Even if your labels came with an alignment jig and the label is properly centered, the other problem is that given enough time, the label adhesive will begin to dry out. When that happens, it's almost a certainty that it will be uneven. That results in bubbles and blisters forming as the label begins to delaminate. That throws the DVD out of balance and it begins to wobble. Once it starts to wobble, the servo system that controls the positioning of the laser beam, can no longer track properly, and the DVD becomes unplayable... For that reason, the use of adhesive labels are what we call 'ticking time bombs'. Again to prove the point; burn a test DVD and apply an adhesive label. Place it in a window exposed to the sun with the label side up. Won't be long before the label starts to delaminate.. (Bye Bye DVD !)
Thermal transfer printers print directly on the polymer top protective coat & yield professional permanent results without fading. Direct thermal printing will not result in imbalances or exhibit any of the other maladies associated with adhesive labels if not stored properly. Though permanent and more resilient, the downside is that they are also not as "pretty" as a full color inkjet printed adhesive label.
The best approach by far is to purchase white inkjet printable media and an inkjet such as the Epson R series of printers that will print directly onto the DVD.
Unlike CD's, DVD's have both a lacquer as well as a polymer top coat. Thus it's perfectly safe to use a Sharpie® permanent marker on DVD's.
DVD Structure & Layout for Video DVD's
This is far from being an in depth discussion
of DVD file structures,
but will give a basic understanding of how a DVD is organized.
A movie DVD is really not much different than a data DVD, in the sense that both contain data files. A movie DVD however, follows a very specific file format and file naming conventions.
Before the DVD is finalized, the file structure is not windows/pc compatible and can only be read by the burner that recorded it. Upon finalization, the DVD burner then generates a Video TS folder that complies with the Windows file structure allowing the files to be read on a computer.
To see how a DVD is structured, just place your finalized DVD in your computer's DVD drive. Right click and select open to explore the file structure on the disc. You'll notice one or possibly two main directories:
11.07.2003 11:20 <DIR> AUDIO_TS (TS stands for Title
Sets) - this directory may be absent on newer DVD's.
11.07.2003 13:55 <DIR> VIDEO_TS (This directory must always be present for video DVD movies)
AUDIO_TS contains only audio files or may be an empty
folder. In the case of newer DVD's this folder may be completely absent ! *
VIDEO_TS contains ALL the data (video as well as audio, for the playback of movies)
* Note: The initial DVD standard called for a folder called the AUDIO_TS in cases where the DVD was to be used only as an audio storage medium. Later standards abandoned it's use. Some older DVD Players however, are expecting to see a separate AUDIO_TS folder. Even although the folder may be empty and not even used, the player will throw a fit if it can't find the folder. Note that most new DVD's in fact, won't even contain an AUDIO_TS title set. Some authoring software packages include it for backwards compatibility with older players, though most newer commercial DVD's have dropped it altogether. If you have one of these ancient players, it's probably time to upgrade anyway....
Since the AUDIO_TS directory is being phased out anyways, we won't delve into it.
There are 3 basic File Types: (actually, only two - as BUP files are identical copies of the INF files)
VOB Files (Video Objects - these files are your actual video content)
INF Files (Information Files)
BUP Files (Backup Files)
The VOB files contain the body of the movie if you will. The data contains both video, audio as well as subtitle information data streams - all interleaved together. All video by standard, is compressed MPEG-2, while the standard audio format is normally AC3 (also known as Dolby Digital). AC3 streams may have a bit-rates between 192 and 448kbit/sec. 192kbit/sec is used for standard 2 channel stereo, while 384-448kbit/sec is used for 5.1channel surround sound.
A VOB contains one primary video stream but may also contain several multi-angle streams for example, thus allowing the selection of different perspectives. The only limitation, is that the maximum bit-rate of the video streams is 9.8mbits/sec while combined video & audio must always be below 10 mb/sec. Up to 9 different audio streams and up to 32 different subtitle streams are also supported.
Also, any single VOB file must never be greater than 1 GB in size for compatibility with set top players (The 1 GB max file size is not a hardware limitation, but rather is the maximum agreed on VOB file size set forth by the DVD standards committee). Thus many movies may contain & span several VOB's - as a single 1gb VOB file will hold only approximately 27 minutes of material if recorded in the SP mode. VOB files larger than 1gb may play ok on your computer, but playback on most standalone players is doubtful.
VOB Files are further broken down by their purpose and how structured by the authoring software.
For example: The VIDEO_TS.VOB files contain the initial DVD opening "splash" screen and menu options. The large VOB files are normally those containing the body of the program.
A DVD may have multiple chapters: Each chapter is designated by a file name of VTS_X. Thus Chapter 1 would be in VTS_01_0.VOB, Chapter 2 in VTS_02_0.VOB etc etc..... The VTS_01_0.VOB and the VTS_01_1.VOB files for example, contain the audio/video that will play for the first chapter.
IFO Files (Information Files)
IFO Files serve as a directory that the player uses to determine where a chapter starts or where a certain audio or subtitle stream is located . It is for this reason that a separate IFO & BUP file is created for each chapter (the naming conventions should be by now, quite obvious)
The IFO files all contain a data structure known as VMGM_MAT that must be present in the VIDEO_TS.IFO files. The IFO files contain much more than just where things are located though..... It tells the player how many chapters are present, # of angles available, where to find the streams, cell addressing & Cell ID, bit padding used etc etc. In a sense it's a complete dossier on the DVD - how it's laid out, how to read it and where the data streams can be found. Loss or corruption of an INF file, results in the entire DVD being rendered unplayable......
BUP Files (Backup Files)
The BUP Files are nothing more than backups of the critical INF Files in case of damage. Should an INF file be corrupt, the disc would be rendered unplayable, as without any way of knowing where the streams are located or even how to play the DVD, the player software would be lost. Thus in the case of a CRC read error of an INF file, the player software will automatically default to using the backup file. If you managed to cleverly clobber both the INF AND the BUP's, then the DVD is "history" - even although the main VOB files containing the program material are fine.
Since VOB files are nothing more than glorified MPEG-2's, renaming them to .mpg may allow playback of a damaged disc on your computer, as most MPEG-2 players will happily play them. If that's successful, then the VOB's can be re-ripped and new INF and BUP's generated by re-authoring. Somewhat of a hack, but all may not be lost !
Note that each title has a minimum of at least 2 VOB's (one for the menu and one for the main feature) and exactly one IFO and one BUP file.
There are many excellent technical articles on the web, delving into the specifics and structures of these files
So why can't I just copy and burn the files to another DVD under windows and make a perfect copy ?....
A file's a file, right ?
Well.... yes and No....
First Some Historical Background...
The DVD's first introduction, the industry realized that illegal copying would be a "sticky" if not expensive legal issue. To avoid such entanglements and allow the development of the DVD without constant lawsuits driving the manufacturer's into bankruptcy, a copy protection scheme had to be employed that would be incorporated into every DVD that allowed full copying of your own files, but blocked any copy attempts of protected material such as commercial movies and the like. The final agreed on encryption technique was called the Content Scrambling System or CSS for short. The CSS is an integration of DVD layout, and embedded CSS chips incorporated into each DVD drive. To effect the standard, all DVD manufacturer's had to be licensed by the Copy Control Association, a non-profit legal entity set up by mutual agreement of hardware manufacturers, artists and the recording industry. This is not as devious as it might first appear, as without such a mechanism in place, DVD burners would never have come into existence !
CSS does not affect the use or copying of unprotected files - only copyright material. It's employment unfortunately thwarts efforts to make a single legal backup copy of a DVD for archival purposes. But aside from this minor inconvenience, the employment of CSS is a welcomed feature that allowed the DVD to become a high quality distribution/storage medium serving a wide range of applications
DVD Encryption Systems
CSS: Content Scrambling System
Unlike regular files, CSS encrypted files cannot be read and displayed directly from the DVD. Instead, one of 400 unlock or encryption keys assigned by the Copy Control Association, must be read from the DVD. This key is then used by the CSS chip embedded in each & every DVD Drive, to effect decrypting of the scrambled DataStream. It is a system that depends on an integration of the physical DVD itself and how its' laid out, and the implementation of descrambling microcode built in to each DVD drive. EXACTLY how the system works in detail, is a closely guarded secret, but here is the gist of it.
Each CSS protected DVD is encrypted with one of 400 keys - meaning that the DataStream of any CSS protected DVD can only be scrambled one of 400 different ways, which is more than adequate. So why when I copy a DVD won't the unlock key obviously recorded on the DVD be copied to the new DVD as well, you might ask ?
The inner most track towards the hub contains the key. By agreement ALL DVD Drives can only read from this restricted area, but can never write to it, thus thwarting any attempts at copying the key.
So although the VOB, INF & BUP files may be freely copied like any other file, the unlock key required to properly decode them, cannot.
The Content Protection for Recordable Media mechanism - is a relatively new scheme supported by all DVD recorders released after 1999 .
This scheme employs something known as the "Burst Cutting Area". The BCA is a reserved area close to the DVD hub where a bar code is burned during DVD manufacture for additional media identification. The BCA can be written ONLY during the mastering process consisting of anywhere from 12 to 188 bytes. This effectively constitutes a serial number, making that physical DVD unique. When used in conjunction with CSS, the proper key could only be derived by reading from the master disc.
This is a Serial Copy Management System (SCMS) designed to prevent copies of copies. In some cases, content providers will allow one copy to be made for backup or archival purposes, but will prohibit copies of copies being made. The CGMS data is embedded in the outgoing video signal much like a digital watermark. Unlike CSS, not all equipment supports CGMS.
This is an Analog Protection System originally devised for "scrambling" the composite output on VCR's. The producer of the disc pays Macrovision royalties to use & license the technology. The composite output on some DVD players are also Macrovision protected. This scheme typically introduces a small instability into the vertical interval small enough such that standard playback on a monitor is achieved, but enough instability to confuse the servo system on recording equipment.
DTCP Digital Transmission Content Protection
A proposed standard whereby content is marked with standard CGMS flags of "Never Copy" or "Copy Once". With this protocol, devices that are digitally connected, such as a DVD player and a digital TV, can exchange keys and authenticate certificates to establish a data pathway. Whether this is ever widely adopted remains yet to be seen
DVD Region Codes - Code Free DVD Players
The film industry imposed an additional encoding technique to be invoked by the various manufacturers, to prevent the latest movies from reaching countries where a particular film has not yet reached the theaters. This regional coding scheme uses a digital designator on the DVD that tells the DVD player for which of the 6 world markets the DVD is intended for and prohibits playback if not a match.
A normal DVD player can only play discs designated for the player's own particular region. However, a code free DVD player is capable of playing DVD discs from anywhere around the world. So while a standard DVD player can only play DVD's from one region, a code free DVD player can play DVD discs from all 6 regions.
Most DVD players sold in the US will play back Region 1 NTSC DVD's only. Multi region players will play back any region encoded DVD - even PAL ! (But not SECAM). Some models even have a built in PAL to NTSC converter that allows playback of Region 2 PAL DVD's on a standard American NTSC TV.
Region 1 - USA, Canada
Region 2 - Japan, Europe, Middle-East, South Africa
Region 3 - South Korea, Hong Kong, Taiwan
Region 4 - New Zealand, Australia, Mexico, South America
Region 5 - Former Soviet Union, Africa, Indian Sub-Continent
Region 6 - China
Note: Very few of the large electronics outlets sell modified code free DVD players. There are numerous sites on the web that specialize in multi-standard video equipment that do however. For the slight additional cost, a code free player is probably the way to go, especially if you swap family video with relatives in Europe or Asia - or just desire unlimited flexibility.
Also, just because a DVD player is billed as being "region free", that is not meant to imply that it will convert PAL signals to NTSC or vice versa. Though some models have built-in standards converters, most do not. Thus without a built in converter, a Region Free player, for example, will play a Region 4 PAL video, but you'll need a PAL monitor to view it !
If the DVD is not copy encrypted, you can in fact freely copy DVD VOB files like you would any other file. If encrypted, you can still copy the files, but the data that make up the files are scrambled and the "key" to decrypt them cannot be copied .
The DVD's and CD's that we burn with your material, are not copy protected, encrypted or region encoded in any way. Thus with the appropriate standard commercial software such as Roxio or Nero, you will be able to make your own perfectly cloned copies.
What's the difference between DVD's recorded in XP (1 hr mode) as opposed to those recorded in SP (standard 2 hr mode) ?
Most DVD's are recorded in SP mode which allows up to 2 hrs of quality video to be recorded on a standard 4.7gb DVD. SP mode offers a nice balance between quality & recording time. XP recording mode employs only half the compression as that of SP encoded files, resulting in even higher quality recordings with less artifacting and "mosquito noise" endemic to all MPEG2 codec's, but limited to 60 minutes. Both SP and XP compression delivers high quality video. The highest compression ratios allow up to either 4 or 6 hours to be recorded on a standard 4.7GB DVD, however image quality starts to really suffer at those high compression levels. As such, we never burn DVD's at those settings..
As far as the DVD's themselves are concerned, there's no difference between an SP and a XP DVD-R. Physical specifications, track pitch, transfer bandwidth etc are exactly identical..... Only the compression used to create the digital data stream is different, which in no way affects playability in a DVD-R player that's working properly. Any player that supports the DVD-R or +R format as appropriate, will play either equally well.
the most comprehensive site concerning all aspects of DVD's by Jim Taylor.
Be sure to check out DVD FAQ....... It's a large download but well worth the wait !
Links: DVD De-Mystified DVD FAQ
Most new DVD players support the DVD-R & +R formats. The operative word is is "most". Just because it's new, does not necessarily mean it supports all the common formats.
DVD-R Help is a site dedicated to providing info on which models support the various formats. It's the most comprehensive site we've found that's up to date concerning DVD-R compatibility.
Before rushing right out and purchasing a new DVD-R capable player based solely on this list, be advised that the site is maintained by user reports only, and although found to be highly accurate, accuracy is not guaranteed and is to be referenced at your own risk. Neither Video Interchange nor Dvdrhelp.com assumes any liability for inaccuracies. Before purchasing any DVD player, the fail-proof "acid test", is to bring a DVD-R along and actually try it in the machine your interested in purchasing.
dvdrhelp.com's DVD-R Player Compatibility List
Blu-Ray vs HD
In the heated format war, Blu-Ray has been declared the winner !
So what's coming after HDTV and Blu-Ray ???
No sooner has Blu-Ray been declared the winner, than a new, even much higher HD standard been proposed by NHK in Japan. It's still in the very early experimental stages... Whether this one wins the next format war, is far too early to tell, since at present, it's the "only kid on the block"... but if history is any lesson, competitive forces after the lucrative pie, will almost surely develop.
Consider the specs....
7680x4320 pixel resolution (about 33 megapixels) at 60 frames/second (that's 4x as high and 4x as wide as HDTV's paltry 1920x1080, or an impressive 16 times the pixel density)
Audio: 22.2 - a new surround standard that blows away anything on the market...... 24 speakers arranged in 3 layers (and you thought 5.2 was impressive !)
Don't hold off on HDTV or Blu-Ray waiting for it's release though. This technology is still likely more than a decade away.
Last Modified: April 22, 2011
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