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Musica Film - Vendita online di DVD musicali e DVD film.
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Technical info

What is a DVD?

DVD stands for Digital Versatile disc (originally Digital Video Disk), and it's, de facto, the successor of Cd - Rom: an advanced optical storage support similar to Cd, but with a far greater capacity (up to 17 Gigabyte compared to 640 Megabyte of a standard Cd-rom).

A Dvd can have up to two overlapped informations layers, as well as two readable sides. The combination of these two factors determines a Dvd disc maximum capacity, which can be 4.7 Gigabyte (for a single - sided, single layer disk), 8.5 Gigabyte (for a single - sided, double layer disk), 9.4 Gigabyte (for a double - sided, single layer disk) or 17 Gigabyte (double - sided, double layer) for disks with a diameter of 12 cm.

Dvd disks are divided into four basics categories, that is Dvd-Video, Dvd-Audio, Dvd-Rom and Dvd-Rewritable. All formats share these common caracteristics: size (diameter is always 12 cm.); possibility of skipping/instant search forward and backward directly up to the chosen point (like a common Cd - Audio); resistence to heat and lack of susceptibility to magnetic fields.

Dvd Videos are commonly used for distribution of movies and musical films (promotional videos, live concerts), along with documentaries and other suitable contents.

In order to read a Dvd-Video, a player (connected to any television or installed in a computer) is required.

A Dvd-Video usually presents a menu, which allow the user to select and regulate various details, like language and audio quality, display of subtitles in different languages, direct access to movie scenes (chapters) or even extra features such as info on performers, additional footage, interviews, making of, games and much more. The Dvd-Video can hold up to two hours of high quality digital video (more than 8 hours on double sided dual layer DVDs) and supports widescreen both on standard and 16:9 televisions. It can manage up to 8 digital audio streams, 32 karaoke tracks or subtitles and 9 camera angles (different viewpoints of a same scene), which can be selected during playback.

Other DVD types

Dvd Audio has been launched and endorsed by record companies looking for a way to prevent piracy and unauthorized duplication. Audio capacities of a Dvd-Video would be, in fact, more than sufficient to guarantee an auditive quality far greater than those allowed by a common Cd, while the copy protection system is named "digital watermark". It consists in a noise pattern (inaudible to human hearing) that allow the player to know if the disc is a copy. Actual Dvd-Video players are usually able to read and play Dvd-Audio too.

Dvd-Rom is the format created for computers. The main advantage is in software distribution: even in its simplest version (single sided - single layer) this kind of disc can hold up to 4,7 GB (4.700 MB) of informations, compared to the 650 MB of a Cd-Rom. Thus, with a DVD writer is possible to store on a Dvd Rom a high amount of data.

DVD-Rewritable offers instead the possibility to store on an optical support, through apposite DVD writers, huge amounts of data. There are, anyway, four recordable versions of Dvd: Dvd-R or +R, Dvd-Ram, Dvd-Rw and Dvd+Rw. Dvd-R disks can be recorded only once (like actual Cd-R). The three other types can be recorded thousand of times, and are different standards currently competing with each other..

Video formats

The video format indicates the proportion between width and height of the reproduced image. A normal television uses a 4 to 3 ratio; should we watch a movie with a wider format (16:9) and thus without cutting off the sides, we would see two black stripes above and below the reproduced image: this modality is known as "letter box". If we have the availability of a TV with a 16:9 screen, we can enjoy a full screen image.

In cinematographic language ratios are not usually expressed with the aforementioned proportions, but are more often referred to with ratios of equivalent meaning. The two most used formats are 1.85:1 and 2.35:1, respectively called VistaVision and Cinemascope.

4:3

It's the common TV ratio, and the normal broadcast signal as well. A movie shot in a 1.33:1 (4:3) ratio is shown full screen and without any black stripes on a normal television, while the same movie seen on a 16:9 television would have its frames appearing in the middle of the screen, with a black stripe on the right and left side as 'fill-ins'. Anyway, with 16:9 TVs the image would automatically be adjusted to the wider screen. Among films in 4:3 ratio, three more subtypes can named.

Native 4:3

Some cartoons intended for the home video market (and many concerts and musical DVD as well) are in 4:3 ratio. In this case, the DVD doesn't suffer any loss in its quality, because the original format has not been modified.

4:3 Pan & Scan

Some movies are shot in panoramic format, and are reduced to 4:3 ratio by cutting and zooming on the frames. A DVD with this ratio sees its quality reduced, as the original proportions are not respected and many details are cut, losing almost half of his original size in the convertion from Cinemascope (2.35:1) to 4:3.

Wide 4:3 or full frame

Films with this specific format show on the screen more than they should, like parts of the original frames originally cut by the director that are nevertheless visible in these editions. It's by all means, an alteration of the original film, which can compromise the visual equilibrium of the image.

16:9

This term comprises all "panoramic" image formats, that is, those with a size wider than common 4:3.

Cinematographic formats are usually of this category, so movies with this ratio imported to DVD without any alteration are not in 4:3, but in a wider aspect ratio.

16:9 LetterBox

The most common widescreen formats are 1.85:1 and 2.35:1. Bringing images of this kind down to a typical TV 4:3, the frame fills the screen in its width but not in its height, thus leaving a black stripe above and below it.

The image appears smaller than the 4:3 ratio, and has smaller resolution as well, so that this ratio appears more suitable to 4:3 TVs.

16:9 Anamorphic

It's a format thought to counterbalance the limitations of LetterBox format. Video signals are transmitted in an "anamorphic" 16:9: this means that the image is redefined, using a larger number of horizontal lines. This implies a vertical expansion of the image on a 4:3 TV (actors "slimmer" than normal), but fits perfectly to a 16:9 TV, which will automatically stretch the video signal in its horizontal dimension.

Audio formats

Mono

Mono (monophonic) audio only comes out from the central channel. This leaves two possibilities: we are listening to audio transmitted with a 1.0 signal, with information effectively memorized only on the central channel, or to audio transmitted with a 2.0 signal, that is with the very same informations doubled on both the right and the left channel (dual mono). In this case, if a ProLogic decoder is on, the outcome will likewise be a single monophonic central channel, which will take its info from two identical channels.

Stereo

It's the stereophony, a 2.0 signal that only uses the two frontal channels. It features in old movies, during comments and on musical DVDs.

Stereo surround

It's a codified 2.0 track from which the Dolby Pro Logic decoder reconstructs and reproduces (with some inaccuracies) a central and a rear channel, which will be therefore split onto two surround speakers.

2.1

Same as previous case, but with a channel exclusively dedicated to the reproduction of low frequencies (this is expressed by the ".1" tag).

4.0

There are two distinct cases that deal with the possibility of just four active channels. The first one sets up three separate frontal channels plus a mono channel separated into two surround speakers.

The second one sets up two stereo frontal channels, two stereo rear channels ad a completely mute central channel.

4.1

Same case as the previous one, except for a channel exclusively committed to the reproduction of low frequencies (as indicated by the ".1" tag).

5.0

Five separate and independent channels: one central, two frontals and two rear.

5.1

Same as above, except for a channel exclusively committed to the reproduction of low frequencies (as indicated by the ".1" tag).

Audio formats

Dolby Digital

The main DVD audio standard. It's a coding system that compress a digital audio stream which subsequently has its amount of necessary data hugely reduced, with only the slightest quality loss. The compression rate can thus reach up to 13:1. Almost all reviewed DVDs contains Dolby Digital codified tracks, and most often in 5.1 digital sound.

Dolby Digital only indicates the compression algorithm, and it's not synonimous of multichannel coding. Dolby Digital, in fact, it's a scalable format and it's possible to codify signals from mono to the complete 5.1.

MPEG audio (stereo or Multichannel)

Just like Dolby Digital, many different configurations are available. Among them, the most common are 2.0 Stereo Surround and 5.1. All channels work the same way as Dolby Digital.

linear PCM

It's the audio standard also used for audio Cds. It's not a complex format and therefore takes more space than a Dolby Digital track.

DTS

DTS (Digital Theatre System) is the multichannel surround coding competitor of Dolby and has been created by Universal Pictures as a new multichannel system for cinemas (and later developed in its "Home" version). The first movie with a DTS soundtrack (paired with analogic Dolby Stereo) was Steven Spielberg's "Jurassic Park". Nowadays, almost all productions share this coding. DTS, in itself, is optional in a DVD. Nevertheless, almost all DVDs include this type of surround sound, which is implemented in any home theater system.

THX

THX is not a format, but a certificate. Lucas Entertainment Ltd., founded by George Lucas (the creative mind behind "STAR WARS" movies), feeling that Dolby Surround inner quality was not enough, has set quality parameters: whose who respect them are given the THX (Thomlinson Holman Experiment) certification. The THX brand, along with audio parts, provides quality controls for video parts, checking definition and color saturation, frame by frame.

Regional codes

DVDs are codified according to the area where they are meant to be distributed

Regional codes

Europe belongs to region 2, together with Middle East, Japan and Sudafrica. Thus, by buying a DVD player in Italy (region 2), we could only watch movies bought in Teheran, Tokyo, Johannesburg or Baghdad, besides of course those coming from Paris, London, Berlin and any italian city (all coming with the "Region 2" code). On the contrary, inserting in the DVD player a disc from New York, the display will show a "region error". Reasons for this limitations are various. One one side, recording industry can better fight DVD piracy when this is restricted to single "regions" and not worldwide; on the other side, they thus reintroduce by other means restrictions that technology has made obsolete. With multistandard televisions or PCs able to read all video formats, everybody through a DVD could watch everything coming from everywhere, as format differences between countries would be annihilated. Codes are meant to prevent that, primarily because movies don't come all on the market at the same time, and the chance to watch on one's television a movie that still has to go on the silver screen in that specific country would lead to uncontrolled consequencies in movie industry. These restrictions, however, are easily bypassed through a small modification of the DVD player, which is legal but invalidates the warranty (in case of a common DVD player), while DVD-ROM protections are often made useless by simple software update.

DVD glossary

AC-3

Stands for Audio Code 3, whose commercial name is Dolby Digital, and suggests a compression protocol for audio signals which, cleverly using psychoacoustic phenomena, allows to obtain an enormous reduction of data, while respecting the overall quality of the original signal. This algorithm can be applied to 5.1 multichannel signals, as well as mono and stereo signals.

Anamorphic

So is named the compression process of images with an aspect ratio of 1.78: or more, in order to resize them to the standard 1.33:1 TV format. Images are therefore expanded to their original size on a monitor with wider screen. Artifact is a generic term used to indicate any kind of imperfection visible or audible on a DVD, and it's usually (but not always) caused by errors occurred during digital compression.

Aspect ratio

The width-to-height ratio of a television screen. Most televisions have a 4:3 aspect ratio. DVD offer 4:3, letter box and 16:9 aspect ratios.

Bit Rate

Indicates the speed of data, first processed by DVD player optical pick up and then sent to the decoding circuitry. In a DVD, that is in MPEG2 standard, bit rate changes every instant: the maximum rate is circa 10Mbit per second (see) while the average for a 130 minutes movie is around 5Mbit per second. Some DVD player can display instant by instant bit rate, thus showing the compression level in any given point of the movie.

Book

Every book specifies a given optival support format. For instance, standard for CD audio is described in the Red Book and CD Rom has its standard described in the Yellow Book. In case of DVD, they are Book A for DVD-Rom, Book B for DVD Video, Book C (only recently defined) for DVD Audio, Book D for DVD-R and Book-E for DVD RAM and RW (yet to be defined).

Buffer

An integrated circuit, which temporarily stores information before they are elaborated. In the case of a DVD, images are grouped in packages, formed by groups of images stored together in the buffer. The buffer then assembles the entire images before releasing it and allowing the image elaboration.

Camera Agles

Camera angles: sequences forming the movie can be shot from different viewpointes, which means different camera positions. DVDs allow the director to memorize - according to his desire - up to nine different camera angles. The viewer will then have the chance to select his favourite perspective. This confers a far greater level of interaction to movies, sport events and didactic videos.

Regional code

Every DVD is encrypted according to region codes, depending on the world area in which that DVD is meant to be commercialized. World is divided in 6 geographical regions and the regional code of a DVD disc must match that of the player. Europe, together with Japan, Sud Africa and Middle East, belongs to "Region 2", while United States and Canada belong to "Region 1"..

Component Video (YUV)

It's the decoding of elements that compose the video signal, used in professional and consumer sectors. It consists of three elements: Iuma, Y, which represents the lightness of the image, ad two cromatic signals given from signals U (R-Y) and V (B-Y), where R and B are red and blue components of the image. The coding system of DVD images is component video, so player with component output video output don't influence the video signal by any means. The Component Video signal stands out for the purity and detail of its colours, as well as for a low noise level.

Data Stream

The constant stream of informations provided by the decoder. This data stream contains all informations needed to decode and visualize an image.

Decoder

Strictly speaking, the decoder is a circuit that transform a stream of conveniently packaged, encoded and/or compressed data in a signal, always digital but suitable to be processed from the d/a converter and then amplified and/or diffused. The word decoder is also commonly used to define the physical device that decodes and amplifies the multichannel audio signal.

Dolby Digital

see AC-3.

Dolby Digital 5.1

Coding or compression system that gives back sound in 5.1 separated channels, each able to cover the whole gamma of frequencies. The 5 channels are right, left, central and right and left effect channels. The ".1" tag indicates the channel committed to the reproduction of low frequencies, the subwoofer.

Dolby Pro Logic

An active decoding system for signals codified in Dolby Surround. From stereo signals it's possibile, thanks to Dolby Pro Logice decoding, shift to a four channel system (right, left, central and surround) altough they are not completely distinct: it always remains a certain level of diaphony, impossibile to quit. The system operates an active decoding (thanks to a microprocessor) of a stereo signal, in order to locate the position of a image within a sonic scene, exploiting phase rotation of the signal vector and psycho acoustic phenomena.

DSP - Digital Signal Processing

Digital Signal Processing. This circuit, within home theater applications, allows to duplicate in one's own house an audio ambient perfectly matching what shown on the screen. Typical "ambient" feature are those who duplicate the acoustic of a theatre, a stadium, a night club or a concert hall. DSP circuit are often already included in home theater amplifiers.

DTS

DTS (Digital Theatre System) is the multichannel surround coding competitor of Dolby and has been created by Universal Pictures as a new multichannel system for cinemas (and later developed in its "Home" version). The first movie with a DTS soundtrack (paired with analogic Dolby Stereo) was Steven Spielberg's "Jurassic Park". Nowadays, almost all productions share this coding. DTS, in itself, is optional in a DVD. Nevertheless, almost all DVDs include this type of surround sound, which is implemented in any home theater system.

DVD-R,DVD-RW

The "-" format is one of the many available DVD formats. By the wording "DVD-R" is meant a record-once writable format, with a storing capacity of 4.7 GB on each layer. The "DVD-RW" format can instead be rewritten more and more times.

DVD+R,DVD+RW

The "+" format is one of the many available DVD formats, with differences that makes it incompatible with "-" format. Nonetheless, by now the majority of players fully supports both formats. By the wording "DVD+R" is meant a record-once writable format, with a storing capacity of 4.1 GB on each layer. "DVD+RW" format can instead be rewritten more and more times.

DVD-RAM

It's the third format, also in terms of consumer popularity. It has a good rewritable capacity and is particularly appreciated in the video editing field.

Encoder

It's an hardware/software combination aimed to codify images and sounds within MPEG2 standard, able to make a real time conversion from the original studio master to a data sequence, which is suitable for a DVD and which will be properly decoded by a DVD player.

Audio streams

In a DVD can co-exist up to eight contemporaneous audio streams, selectables with a remote control. This easily allow the creation of multiple language DVDs, which can be comercialized in different markets.

Gigabyte

Unit of measurement roughly equivalent to a billion bytes and thus to a eight billions of bits. A single sided, single layer DVD can store up to 4,7 gigabyte.

Layer 0 and 1

Layer 0 is, in double layer DVD, the external layer, the one closer to the lens. It's semitransparent and the laser beam can pass through it. Layer 1 is the one below.

Megabit per second

A megabit contains a million of bit. Mbps stands for millions of bit per second or megabits per second and is a measure of bandwidth (the total information flow over a given time) on a telecommunications medium. A DVD Video can reach up to a rate of 10 Mbit per second.

MPEG1

A type of digital signal compression, developed by Moving Pictures Expert Group, an ISO division (International Standards Organization). This system can reach performance of up 30 frames per second, with a compression rate greater than 6:1 and a resolution roughly equivalent to a quarter of that of TV broacasting system. Plainly said, this system is too slow to deal with high quality images.

MPEG2

It's a type of audio video digital compression, able to play back up to 30 frames per second, with a compression rate variable to up to 200:1 To have a broadcast video quality, the compression rate can be reduced to 30:1. MPEG2, fully compatible with MPEG1, is based on the principle of reduction of signal redundancy during the compression phase, in order to later reassemble it during the reproduction phase, through the use of I, B, P frame.

Multiangle

It's the function that allow DVD users to elect between nine different perspectives of a movie sequence, only when possible of course (e.g., the director has decided to include more viewpoints of a given scene).

Multilanguage

A single DVD can contain up to eight different audio track. The user can thus select the preferred audio track simply by pushing a button of the remote control.

NTSC

Acronym of National Television System Committee, it's the name of the television standard adopted by United States.

PAL

PAL system is the european television standard (in France it's the Secam).

Panavision

It's the 2.35:1 screen ratio, obtained by projecting 35mm films (properly recorded) through anamorphic lens.

PCM

Acronym of Pulse Code Modulation. Indicates the standard form used for storing and compressing digital audio, as it happens for instance on CDs and DVDs. It processes audio signals with volume samples generated in continuous time periods. The parameters that define a PCM file are sampling rate and resolution. The superior storage capacity of a DVD allows it to memorize audio signal of far better quality than a common CD. On a DVD can in fact be stored a PCM audio signal with a 24 bit quantization (compared to CD 16 bit) and a sampling sequence of 96 KHz (compared to CD 44,1).

RDSL

It's the acronym of Reverse Spiral Dual Layer, and identifies DVDs with a double layer side. The two layers are recorded in a spiral groove beginning at the outside edge and winding its way to the center (level 0) and then back to the outside edge (level 1), eliminating the need for a complete pickup repositioning. Anyway, the layer change might cause a slight jitter in the movie due to the re-focusing of the lens. This is so short however, that it's barely noticeable on most players, if at all.

Data reduction

The uncompressed digital video signal brings along many unnecessary informations, not needed for the creation of high quality images. Data reduction (compression) algorithms were thus created to permit, without any quality loss, a considerable reduction of necessary data and a quick definition of the image. One of those is the MPEG2, used on DVDs.

THX

THX is not a format, but a certificate. Lucas Entertainment Ltd., founded by George Lucas (the creative mind behind "STAR WARS" movies), feeling that Dolby Surround inner quality was not enough, has set quality parameters: whose who respect them are given the THX (Thomlinson Holman Experiment) certifiaction. THX brand, along with audio parts, provides quality controls for video parts, checking definition and color saturation, frame by frame. Last THX versions are brand new THX ULTRA and THX SELECT.