There are currently four main types of DVD discs, classified by the number of sides (single- or double-sided) and layers (single- and double-layer).

DVD-5 4.7 GB single-sided, single-layer drive. Consists of two substrates connected to each other. One of them contains a recorded layer, which is called the zero layer, the second is completely empty. Single-layer discs typically use an aluminum coating.

DVD-9 8.5 GB single-sided, dual-layer disc. Consists of two stamped substrates connected in such a way that both recorded layers are on the same side of the disc; on the other side there is an empty substrate. The outer (zero) stamped layer is covered with a translucent gold film that reflects the laser beam focused on this layer and transmits the beam that is focused on the lower layer. A single variable-focus laser is used to read both layers.

DVD-10 9.4 GB double-sided single-layer drive. Consists of two stamped substrates connected to each other by their back sides. The recorded layer (zero layer on each side) is usually coated with aluminum. Please note that this type of disc is double-sided; The reading laser is located at the bottom of the drive, so to read the second side the disc must be removed and flipped over.

DVD-18 17.1 GB double-sided, dual-layer drive. Combines two recording layers on each side. The sides of the disc, each formed by two stamped layers, are joined together with their backs facing each other. The outer layers (layer 0 on each side of the disc) are coated with a translucent gold film, the inner layers (layer 1 on each side) are coated with aluminum. The reflectivity of a single-layer disc is 45-85%, of a double-layer  18-30%. Various reflective properties are compensated for by an automatic gain control (AGC) circuit.

The design of various types of DVD discs is shown in Fig. 7.

Please note that although in Fig. Figure 7 shows two lasers reading data from the bottom of dual-layer disks; in fact, only one is used. To read data located on different layers, only the laser focus changes.

There are two ways to record layers of double-layer discs: opposite (OTR) or parallel (PTP) direction of tracks. The OTP method allows you to minimize the time spent reading a disk when moving from one layer to another. When it reaches the inside of the disc (the end of layer 0), the laser sensor remains essentially in the same position and only moves slightly to focus on layer 1. The end area of ​​the disc when it is written in OTP mode is called middle zone.

Res. 7. Types and design of DVD discs

Writing (and reading) to spiral tracks of DVDs recorded in PTP mode works differently. When moving from layer 0 to layer 1, the laser sensor must move from the outside of the disk (ie, the end of the first layer) to the inside (the beginning of the second layer). In addition, the laser focus must be changed. To speed up the transition, almost all DVDs are written in OTP mode.

The direction of the spiral tracks of different layers recorded in the PTP mode also differs. This simplifies the process of reading tracks located one above the other. The spiral track of layer 0 is directed clockwise, and the track of layer 1, in turn, is counterclockwise. Therefore, to read the second layer, you need to change the direction of rotation of the disk, but in OTP disks, the reading of the spiral occurs from the outside to the inside. Thus, the spiral track of layer 0 is directed from the inside to the outside, and the track of layer 1 is directed from the outside to the inside.

The differences between DVDs recorded in PTP and OTP modes are shown in Fig. 8.

The capacity of digital versatile disks depends on their type and reaches 17.1 GB. The capacity of dual-layer discs is slightly less than the capacity of two single-layer discs, even though the layers of the discs occupy approximately the same space (the lengths of the spiral tracks of different types of discs are the same). This was done to improve the readability of disc layers in a dual-layer configuration. The distance between the turns of the tracks was slightly increased, which entailed an increase in the length of the depressions and platforms. To compensate for this, the drive's rotation speed increases when reading a dual-layer disc, resulting in a constant data transfer rate. But since the spiral track is read faster, the overall capacity of the disk is reduced slightly.

In addition to the listed types of standard containers, double-sided discs can also be produced, having one layer on one side and two layers on the other. This type of disc is designated DVD-14 and has a capacity of 13.2 GB or approximately 6 hours and 15 minutes of MPEG-2 video data. There are also 80mm drives that have a smaller capacity than standard 120mm drives of the same configuration.

Double-sided discs are more complex and costly, and require that the disc be removed from the drive and turned over to play both sides. All this has led to the fact that DVD-5 (single-sided, single-layer) or DVD-9 (single-sided, double-layer) discs are most widely used. The capacity of this type of disc reaches 8.5 GB, which is 242 minutes of playback of MPEG-2 video data. With 133 minutes of playback, DVD-5 video discs are suitable for more than 95% of currently available movies.

Res. 8. DVD discs recorded in PTP and OTP modes

This article covers the basic concepts and principles used in creating DVD Video discs. All material is taken from various sources located on the Internet. Where possible, I have provided links to sources of information. If I suddenly forgot someone, please do not be offended and let me know about it.

DVD format

Physically, the DVD format is similar to a CD, with the difference that a laser beam with a shorter wavelength is used to work with DVD discs. Due to this, a high recording density is achieved. Also, there are DVDs with an additional data storage layer, which doubles the amount of data stored on one side. A single-layer DVD can record up to 4.7 GB per side, and a double-layer DVD can record up to 8.5 GB.

There are several types of DVD media. DVD Forum initially defined three types: DVD-R, DVD-RW, and DVD-RAM. DVD-RAM is a physically rewritable format, but it is not compatible with the standard DVD Video format.

Logical organization of DVD Video

Unlike a CD, which consists of tracks listed in a TOC (Table Of Contents), a DVD has a UDF file system.

DVD Video is logically divided into the following parts:

• First-Play Section. Plays first immediately after the disc is inserted into the device
• VMGI (Video Manager Information). Video manager information
• VMGM (Video Manager Menus). Video manager menu
• VTS (Video Title-Sets). Video Application Kits

Each Video Application Suite (VTS) is logically divided into

• VTSI (Video Title Set Information). Video application information containing control data.
• VOB (Video Objects). Menu
• VOB (Video Objects). Data
• VTSI backup

Each VOB (Basic Disc File Unit) includes video, audio, subtitles, and navigation data. When a VOB is played, the player not only plays the video in sequence, but also follows navigation commands to display menus, accept commands from the user, etc. Each VOB includes individual cells linked together using Program Chains. PGC) that provide the required interactivity using a simple programming language designed for DVD Video. PGCs are used to regulate the playback of video, audio and subtitles in VOBs, display menus, and enter and execute user commands. There are three types of PGCs: sequential play, random play and mixed play. Individual cells can be used by more than one PGC, which can define different sequences of video playback, for example to provide seamless branching. PGCs are subject to a set of instructions for elementary programming, including mathematical and logical operators, conditional branches, countdown, etc. etc. There are 16 regular registers for more complex programming, and 16 system registers.

DVD-Video file organization

VOBs and other data are located in the VIDEO_TS directory. The table below shows an example of a disk with one set of video applications.

Audio, video and subtitles can be contained in no more than 9 VOB files related to a given video application, each of which does not exceed 1 GB in size. Thus, while a DVD-5 will have no more than 5 VOB files pertaining to a video application, a DVD-9 may require all 9. The VTS*.* files may be repeated for each Video Application Set (VTS) and will be named VTS_02* accordingly. *, VTS_03*.*, etc. For each VTS there will be one .IFO and .BUP files, plus one or more .VOB files.

Stream Requirements

One of the mandatory requirements of the DVD Video standard for a video stream is that it must be encoded in MPEG-1 or MPEG-2. Thus, to encode video prepared for recording, an MPEG-1 or MPEG-2 codec is required. MPEG-2 is preferable to use because it is more advanced and modern, however, if you need to get an output video stream with a bitrate below 1 Mbit/sec (about 10 hours of video on a standard single-layer DVD media), then in this case it is better use the MPEG-1 codec.

A digital video stream reproduced in the countries of the former CIS must meet one of the requirements listed below, due to the fact that standard DVD players may simply refuse to play a video object if the format of the video stream in it does not meet the specified requirements.

The MPEG encoding process eliminates redundant video data in a series of adjacent frames. Two adjacent frames usually contain many of the same image elements. The information in them differs by a small part from all the information contained in the frame. Video compression is performed, which uses not all the data of each video frame, but the dynamics of frame changes, since in most successive frames of one video plot the background almost does not change, and clearly noticeable changes occur in the foreground. For example, a small object moves smoothly against a constant background. In this case, complete image information is stored only for reference images. For the remaining frames, only difference information is digitized: about the position of the object, the direction and magnitude of its displacement, about new background elements that open behind the object as it moves. Moreover, this difference information is calculated not only in comparison with previous images, but also with subsequent ones (since it is in them that a previously hidden part of the background is revealed as the object moves). Reference frames in an MPEG video stream must be inserted every 15 or 18 frames, due to the fact that it is the reference frames, or I-frames, as they are also called, that are used by video viewers when fast-forwarding or rewinding the video.

To comply with the DVD Video format, the bitrate of the multiplexed stream should not be higher than 9.8 Mbit/s and not less than 300 Kbit/s. This parameter must be taken into account when receiving the final MPEG stream.

Basic concepts and definitions

DVD video. To play DVDs with video, you need a DVD drive and an MPEG-2 decoder (that is, either a household DVD player with a hardware decoder, or a computer DVD drive and a software player with a decoder installed). DVD movies are compressed using the MPEG-2 algorithm for video and various (often multi-channel) formats for audio. The bitrate of compressed video varies from 2000 to 9800 Kbps, often variable (VBR - variable bitrate). The standard video frame size for the PAL standard is 720×576 pixels, for the NTSC standard it is 720×480 pixels. The audio data in a DVD movie can be in PCM, DTS, MPEG, or Dolby Digital (AC-3) format. In countries that use the NTSC standard, all DVD movies must contain a PCM or AC-3 soundtrack, and all NTSC players must support these formats. Thus, any standard disc can be played on any standard hardware. In countries using the PAL standard (most of Europe, including Russia), at first they wanted to introduce PCM and MPEG-2 formats as the audio standard for DVD, but under the influence of public pressure and going against the wishes of Philips, DVD-Forum included Dolby AC-3 to the list of optional audio formats on discs and mandatory formats in players.

PAL (Phase-Alternating Line). An analogue color television system was developed by Walter Bruch, an engineer at the German company Telefunken, and introduced as a television broadcasting standard in 1967.

NTSC (National Television Standards Committee). National Television Standards Committee. Analogue color television system developed in the USA. On December 18, 1953, color television broadcasting using this particular system was launched for the first time in the world. NTSC has also been adopted as the standard color television system in Canada, Japan and a number of countries on the American continent.

MPEG (Moving Picture Experts Group). Moving Image Expert Group. A group of specialists under ISO that meets to develop standards for digital video and audio compression.

MPEG-1. A group of standards for digital audio and video compression adopted by MPEG. MPEG-1 video is used, for example, in the Video CD format. Video CD (VCD) video quality is approximately the same as VHS video cassettes.

MPEG-2. A group of standards for digital coding of video and audio signals approved by ISO - International Organization for Standardization / IEC Moving Picture Experts Group (MPEG). The MPEG-2 standard is primarily used for video and audio encoding in broadcasting, including satellite broadcasting and cable television. MPEG-2, with some modifications, is also actively used as a standard for DVD compression.

Number (frequency) of frames per second. The number of still images that replace each other when showing 1 second of video material and create the effect of moving objects on the screen. The higher the frame rate per second, the smoother and more natural the movement will appear. The minimum indicator at which the movement will be perceived as uniform is approximately 10 frames per second (this value is individual for each person). Traditional film cinematography uses 24 frames per second. PAL and SÉCAM television systems use 25 frames per second (25 fps or 25 Hertz), and the NTSC system uses 29.97 frames per second. Good quality computer digitized video footage typically uses a frame rate of 30 frames per second. The upper threshold frequency of flickering perceived by the human brain is on average 39-42 Hertz and is individual for each person. Some modern professional cameras can shoot at up to 120 frames per second. And special cameras for ultra-fast shooting shoot at a frequency of up to 1000 frames per second and higher, which is necessary, for example, for a detailed study of the trajectory of a bullet or the structure of an explosion.

Interlace scanning. Scanning of video material can be progressive (interlaced) or interlaced. With progressive scan, all horizontal lines (lines) of the image are displayed simultaneously. But with interlaced scanning, even and odd lines (also called frame fields) are shown alternately. Interlaced scanning is often called interlacing or interlacing in English. Interlace scanning was invented to display images on picture tubes and is now used to transmit video through “narrow” channels that do not allow the image to be transmitted in full quality. PAL, SÉCAM and NTSC systems are all interlaced scanning systems. New digital television standards, for example, HDTV, provide progressive scan. Although technologies have appeared that allow simulating progressive scanning when displaying material with interlace. Interlace is usually indicated by an "i" after the vertical resolution, such as 720x576ix50 for PAL video. To suppress the unpleasant effects that occur when viewing interlaced video on a progressive screen, special mathematical methods called deinterlacing are used.

Progressive scan. Unlike interlaced scanning, where only half of the image is formed per frame (either even or odd lines), with progressive scanning the entire image is formed, i.e. all lines. Currently, interlaced scanning is used only in cheap CRT televisions.

Deinterlacing The process of creating one frame from two interlaced half-frames for display on a progressive scan screen such as a computer monitor. Used in computer video processing systems, flat panel TVs, etc.

Permission. By analogy with the resolution of computer monitors, any video signal also has a resolution, horizontal and vertical, measured in pixels. Typical analogue television resolution is 720x576 pixels for PAL and SÉCAM standards, at a frame rate of 50 Hertz (single field, 2x25); and 648x486 pixels for NTSC, at 60 Hertz (single field, 2x29.97). In the expression 648x480, the first number indicates the number of points in a horizontal line (horizontal resolution), and the second number indicates the number of lines themselves (vertical resolution). The new standard for high-definition digital television HDTV offers resolutions of up to 1920×1080 at a flickering frequency of 60 Hertz with progressive scan. That is, 1920 pixels per line, 1080 lines.

Number of colors and color resolution of the video signal. Described by color models. For the PAL standard, the YUV color model is used, for SÉCAM the YDbDr model, for NTSC the YIQ model, in computer technology it is mainly used RGB (and αRGB), less often HSV, and in printing technology CMYK. The number of colors a monitor or projector can display depends on the quality of the monitor or projector. The human eye can perceive, according to various estimates, from 5 to 10 million shades of colors. The number of colors in video material is determined by the number of bits allocated to encode the color of each pixel (bits per pixel, bpp). 1 bit allows you to encode 2 colors (usually black and white), 2 bits - 4 colors, 3 bits - 8 colors, ..., 8 bits - 256 colors, 16 bits - 65,536 colors, 24 bits - 16,777,216 colors. In computer technology, 32 bits per pixel (αRGB) is standard, but this additional α-byte (8 bits) is used to encode the pixel's opacity (α), rather than color (RGB). When a pixel is processed by the video adapter, the RGB value will be changed depending on the value of the α-byte and the color of the underlying pixel (which will become “visible” through the “transparent” pixel), and then the α-byte will be discarded, and only the RGB color signal will go to the monitor .

Bitrate. The width (otherwise known as speed) of a video stream or bit rate is the number of processed bits of video information per second of time (denoted “bit/s” - bits per second, or more often “Mbit/s” - megabits per second; in English designated “bit/s” and “Mbit/s” respectively). The higher the video stream width, the better the video quality in general. For example, for the VideoCD format the video stream width is only about 1 Mbit/s, and for DVD it is about 5 Mbit/s. Of course, subjectively the difference in quality cannot be assessed as fivefold, but objectively it is so. And the HDTV digital television format uses a video stream width of about 10 Mbit/s. Using the video stream speed, it is also very convenient to evaluate the quality of video when it is transmitted over the Internet. There are two types of stream width control in a video codec - constant bit rate (CBR) and variable bit rate (VBR). The VBR concept, now very popular, is designed to preserve video quality as much as possible, while reducing the total volume of the transmitted video stream. At the same time, in fast scenes of movement, the width of the video stream increases, and in slow scenes, where the picture changes slowly, the width of the stream decreases. This is very convenient for buffered video broadcasts and transmission of stored video material over computer networks. But for bufferless real-time systems and for live broadcasting (for example, for teleconferences) this is not suitable - in these cases it is necessary to use a constant video stream speed.

Screen aspect ratio. The aspect ratio of the frame is the most important parameter in any video material. Since 1910, motion pictures have had a screen aspect ratio of 4:3 (4 units wide by 3 units high; sometimes written as 1.33:1 or simply 1.33). It was believed that it was more convenient for the viewer to watch a film on a screen of this shape. When television appeared, it adopted this ratio and almost all analogue television systems (and therefore televisions) had a screen aspect ratio of 4:3. Computer monitors have also inherited the television standard of the parties. Although back in the 1950s, this idea of ​​4:3 changed radically. The fact is that the human field of vision has a ratio of not 4:3. After all, a person has 2 eyes located on the same horizontal line - therefore, a person’s field of vision approaches a 2:1 ratio. To bring the frame shape closer to the natural field of view of a person (and, therefore, enhance the perception of the film), the 16:9 (1.78) standard was introduced, almost corresponding to the so-called “Golden Ratio”. Digital television also mainly focuses on the 16:9 ratio. By the end of the 20th century, after a number of additional studies in this area, even more radical aspect ratios began to appear: 1.85, 2.20 and up to 2.35 (almost 21:9). All this, of course, is designed to immerse the viewer deeper into the atmosphere of the video being watched.

PCM. Pulse code modulation (PCM or Pulse Code Modulation) is used to digitize analog signals before transmitting them. Almost all types of analog data (video, voice, music, telemetry data, virtual worlds) allow the use of PCM modulation. To obtain a PCM modulated signal from an analog signal at the input of the communication channel (transmitting end), the amplitude of the analog signal is measured at regular intervals. The number of values ​​digitized per second (or digitization rate) is a multiple of the maximum frequency (Hz) in the analog signal spectrum. The instantaneous measured value of the analog signal is rounded to the nearest level from several predefined values. This process is called quantization, and the number of levels is always taken as a multiple of a power of two, for example, 8, 16, 32 or 64. The level number can be respectively represented by 3, 4, 5 or 6 bits. Thus, the modulator output produces a set of bits (0 or 1). At the receiving end of the communication channel, the demodulator converts the sequence of bits into pulses with the same quantization level that the modulator used. These pulses are then used to restore the analog signal.

The DVD standard implies recording images with the aspect ratio adopted in television broadcasting, i.e. 3:4, or, in another way, 1.33.

There are several video standards around the world:

PAL- video standard used in Europe and Russia (i.e. ours): video size 720x576, 25 fps (25 frames per second).

NTSC- 720x480, 29.97 fps.

There is also a standard SECAM, which concerns television broadcasting.

VHS- analog video is a recording format on your video tapes.

DV (Digital Video) is a video format jointly developed by the world's leading video production companies for digital recording. This format has a low video compression ratio (5:1) and provides high quality video recording. MiniDV cameras shoot video in this format.

D.V. the format is characterized by a large video stream and, accordingly, has a large output video file. An hour-long recording on a MiniDV cassette will have a volume of approximately 12 GB, or 1 minute - 200 MB.

The resulting video must be compressed for later viewing on a computer, projector, DVD player, or on the Internet. Those. From the resulting high-quality video we can obtain any format we need of appropriate quality.

Attention! Not to be confused with DVD (Digital Video Disc) - this is a disk with digital information, what we call a DVD in life.

Compression standards:

MPEG- one of the main compression standards. The abbreviation MPEG (Moving Pictures Expert Group) is the name of the international committee involved in the development of this compression standard. Its varieties:

MPEG-1- compression format for compact discs (CD-ROM). The video quality is the same as that of a regular VCR, resolution 352x240; a disc with a film in this format is usually designated VCD (VideoCD).

MPEG-2- format for DVDs, digital television. DVD, HDD, and Flash cameras shoot video in this format.

MPEG-3- not currently used. Do not confuse it with MP3 (MPEG Audio Layer 3) - audio compression technology!

MPEG-4 is a format obtained using the well-known codecs DivX, XviD, H.264, etc. It is often simply called MP4. It reduces the video stream even more than MPEG-2, but the picture is still of decent quality, so this format is supported by most modern DVD players. Of particular note is the high quality of video compressed with the latest generation H.264 codec.

HD (High Definition)- high-resolution format, a new format of special image clarity. It has two varieties: HD1 with a resolution of 1280x720 and HD2 - 1440x1080.

Video formats:

AVI (Audio-Video Interleaved) is an extension for a huge number of video files, but is not a format or codec. This is a container developed by Microsoft that can store 4 types of streams - video, audio, text and midi. This container can contain video of any format from mpeg1 to mpeg-4, sounds of different formats, and any combination of codecs is possible. To determine the contents of this container, you need to use one of the many programs from the powerful Adobe Premiere to the simple VideoToolBox.

WMV (Windows Media Video)- this is a format from Microsoft, and it is in this format that you will receive a video made using Movie Maker.

MOV- Apple Macintosh QuickTime format, can also contain graphics, animation, and 3D in addition to video. Most often, QuickTime Player is needed to play this format.

MKV- (Matryoshka or Matroska) is also a container that can contain video, audio, subtitles, menus, etc. It is open source, not very widespread yet, but very promising.

3gp- videos for third generation mobile phones are small in size and low quality.

Let's look at the video formats that are used on the Internet:

FLV(Flash Video) is a video format for posting and transmitting on the Internet, used by such platforms for posting video clips as YouTube, RuTube, Tube.BY, Google Video, Movie and many others.

SWF(Shockwave Flash) is an extension of animation created in the Adobe Flash program, as well as video in Flash format, played by browsers using Flash Player. Flash movies are also widely distributed on the Internet.

This means that the FLV extension is a flash video, and the SWF extension is a flash movie.

RM, RA, RAM- extensions of the RealVideo format from RealNetworks, which is used for television broadcasting on the Internet. It has a small file size and low quality, but allows you to watch, for example, a TV news release on the website of a certain television company.

Let's look at the main extensions that relate to DVDs:

VOB (Versioned Object Base) is a container extension that can contain multiple video (MPEG-2 format) and audio streams, as well as movie menus and subtitles. These are the main files on a movie DVD.

IFO- files on a DVD disc containing information about the film, menu, order of launching VOB files, necessary, for example, for a DVD player, i.e. service files. Created during the conversion or authoring process, i.e. burning a DVD.

m2v, m2p- video extensions in MPEG-2 format. I won’t go into depth, I’ll just say that such a video is needed for authoring, i.e. creating VOB files and burning DVDs. I'll talk about authoring elsewhere.

DVD video.

Physically, the DVD format is similar to a CD, with the difference that a laser beam with a shorter wavelength is used to work with DVD discs. Due to this, a high recording density is achieved. Also, there are DVDs with an additional data storage layer, which doubles the amount of data stored on one side. A single-layer DVD disc can record up to 4.7 GB per side, and a double-layer DVD can record up to 8.5 GB.

There are several types of DVD media. DVD Forum initially defined three types: DVD-R, DVD-RW, and DVD-RAM. DVD-RAM is a physically rewritable format, but it is not compatible with the standard DVD Video format.

With ordinary CD discs everything is simple: they are either CD-R (Compact Disc Recordable), i.e. write-once discs, or CD-RW (Compact Disc Rewritable) - rewritable discs. But with DVDs it’s more complicated - there are many types of DVDs, and it’s easy to get confused in such a variety.

Let's start by deciphering the abbreviation DVD. Previously, the abbreviation DVD stood for Digital Video Disc, since the first DVDs were designed to record video only. Then, when it became possible to record other types of data on DVD, DVD was "renamed" Digital Versatile Disc - Digital Versatile Disc.

Essentially, DVD is a development of CD technology, but first things first. The history of DVD can be considered to have started in 1994, when Sony, Philips and Toshiba began creating a new storage medium. In general, Hollywood was the initiator of all this - ordinary video cassettes did not provide any means of protection against unauthorized copying. And the alternative media available at that time (CD) did not provide the proper quality of video playback - it was impossible to record a film of normal quality on a regular 700 MB disk. At least two disks were required.

In 1996, Sony, Philips and Toshiba introduced the first specifications for a new storage medium - DVD-ROM (the base format used for storing data) and DVD-Video (a superstructure on the DVD-ROM format, designed for storing video). DVD was then mainly used to store video, which is why it was called Digital Video Disc.

In 1998, a new format was introduced - DVD-Audio. Since the DVD format was already used not only for storing video, in order not to introduce a new abbreviation and not confuse users, it was decided to replace the word “Video” with the word “Versatile”. In the same year, the DVD capacity was increased to 4.7 GB (originally 4.5 GB). Despite the fact that the DVD-Audio format appeared in 1998, the first DVD players (specifically for the DVD-Audio format) appeared in 2000 and were very expensive. In Europe, such players first appeared in 2001.

Now a new format is beginning to become popular - Blu-Ray. Inexpensive combination drives have appeared, and laptops are increasingly equipped with drives that can read Blu-Ray. But the Blu-Ray format itself was announced back in 2002. Seven years have passed, and the format has not yet gained much popularity.

The most interesting thing is that DVD is an almost ideal storage medium without any particular disadvantages. Judge for yourself. A DVD can record from 4.7 to 18 GB of information (on a double-layer and double-sided disc). Just count how many regular CDs are needed to record at least 4.7 GB.

What about the flash drive? An 8 GB flash drive won’t surprise anyone these days. But a flash drive does have some disadvantages. Firstly, an 8 GB flash drive costs significantly more than a 9 GB DVD-RW. Secondly, due to the desire to save money, there is a high probability of buying a low-quality flash drive that will last less than the most ordinary DVD-RW.

In addition, DVD supports various video formats (4:3, 16:9), multi-channel audio and up to 9 different camera angles. In a word, if you just need to record data, then you can get by with a regular flash drive, but if you need a medium for video, then nothing better than DVD has yet been invented (Blu-Ray is not yet taken into account due to its high cost).

DVD-Video and DVD-Audio support Dolby Digital, Dolby Digital Pro and Dolby Surround (5+1 multi-channel audio) standards, which further adapts them for high-quality sound reproduction (both when watching movies and when listening to audio tracks). And if we add to all this the possibility of interactive control (controlling the sequence of scenes, changing view cameras, calling subtitles, supporting “bookmarks”), then in general DVD has no competitors yet. In this regard, CDs and flash drives are not a competitor, but VHS cassettes are even more so. Plus, VHS tapes are unreliable and huge compared to DVDs.

Previously, the disadvantages of DVD included the high cost of both DVD players and burner drives. Now the prices are so ridiculous that it is not customary to talk about the cost of equipment for recording and playing DVDs. DVD blanks are also cheap, although only those that are single-sided and single-layer, but in any case, storing 4.7 GB on a DVD will cost you less than storing the same amount on a CD.

Besides being expensive, DVDs used to have some compatibility issues. The fact is that, since 1996, various companies have produced so many different formats that some drives could work with some formats, but not with others (or, for example, did not support recording of certain DVD formats). Today this is not the case, and the most common DVD drive can work with all available formats.

Now let's talk about DVD formats. When choosing DVD discs, pay attention to their markings.

DVD disc marking

In addition to markings, the DVD may contain the following inscriptions that define the DVD standard:
• DVD-ROM is the basic format used for mass production of discs. Discs of this format can be purchased already recorded, since the technology for recording them is somewhat different from recording ordinary DVD discs at home.
• DVD-Video is an “add-on” to the DVD-ROM format that specifies the order in which files are placed on the DVD-ROM. In addition to video, such a disc can contain pictures (for example, frames of the most interesting scenes of a film), subtitles in different languages, and dialog boxes for organizing menus.
• DVD-Audio - used to record high-quality sound. After all, sound can be recorded on a regular AudioCD, encoded in the MP3 format, and recorded on a regular CD-R. The sound quality of DVD-Audio is significantly superior to AudioCD and better than DVD-Video (due to the fact that all the space is allocated only for audio, while DVD-Video also has to store video, subtitles and other data). The DVD-Audio format is recognized as the best audio format today.
• DVD-R is a write-once disc. You can record whatever you want on such a disk - music, videos, pictures, data, but only once. Using DVD-R, you can create a DVD-Video or DVD-Audio disc, but without copy protection. To create a disc with such protection, you need a disc for producers - DVD-Authoring. These discs are much more expensive than regular DVD-Rs, and not all drives can burn DVD-Authoring discs. Therefore, before purchasing an expensive DVD-Authoring disc, make sure that your drive supports recording this type of disc.
• DVD-RW is a rewritable DVD disc. As with CD-RWs, you can write information to a disc, then erase it, then write it again, and so on.
• DVD-RAM is another type of rewritable disc. Its difference from DVD-RW is that it is more reliable: if regular DVD-RW can be rewritten about 100 times (we don’t take cheap Chinese ones into account - it’s good if you managed to rewrite such a disc 10 times), then DVD-RAM can be rewritten 1000 times. In addition, DVD-RAM allows you to record a disc track by track, which does not require creating an image of the future disc on the hard drive. After all, it may turn out that you will not have 9 GB of free disk space. The minimum disk space required to record a DVD-RAM disc of any capacity is only 200 MB. But this type of disk also has disadvantages: it is expensive, slow (the writing speed is very low) and basically only computers can read it, but not all household players.
• DVD+R/DVD+RW is a new DVD disc format. The "+" sign in the marking means that the new format is better than the previous one. The advantage is the higher writing speed of such discs. Previously, not all drives could write discs with a plus. Now there is no such problem, and all modern drives can burn discs of both new and old formats. Which drive should I choose? Now there is not much difference. If you want to save money, buy DVD-R/RW - they are a little cheaper (just don't buy the cheapest ones - and don't say later that I didn't warn you!).

DVD-5 and DVD-10 discs are the most common and in demand. Discs in DVD-9 and DVD-18 formats are less common on sale. This is due to the higher cost and the fact that some players (we are talking about household players, not DVD drives) cannot work with dual-layer discs. All modern DVD drives can read and write dual-layer discs, you just need to turn the disc over to read/write from the other side.

Some DVD manufacturers claim that their discs can store information for 50-100 years. Personally, I don't believe such statements - the DVD format appeared in 1996, and not enough time has passed to make such statements. Moreover, given the pace of development of computer technology, in 50 years there will not be a single drive capable of reading DVDs. Remember floppy disks: the last time an FDD drive was installed in my computer was about four years ago. The first floppy disk was produced back in 1971. It was an 8-inch floppy disk made by IBM. And the 3.5" floppy disks that we got used to back in the day (or at least still found them) appeared in 1981 thanks to the efforts of Sony. Floppy disks lasted an average of 25 years. Of course, they are still on sale, you can buy even drives for reading floppy disks, but practically no one uses them anymore. After all, flash drives are more compact and allow you to record more information.

As for DVDs, I would recommend the following: DVDs should be stored in a cool place, away from direct sunlight. It is advisable to store discs in separate boxes, and not on top of each other - then scratches may form on the surface of the disc. Once every two years (or once a year, if you often use these discs), it is advisable to rewrite information from them onto new DVDs, this way you will be safe from data loss.

It is perhaps impossible to meet a person now who has never held a CD in his hands. Recently, these storage media have seriously lost their positions due to the active introduction of more technologically advanced drives based on solid-state memory. Nevertheless, it is still hardly advisable to completely abandon disks.

The DVD capacity is quite sufficient to store most programs and multimedia files. Manufacturers indicate that 4.7 GB is available to the user. In reality, the maximum information capacity is 4.38 GB, which is explained by the difference in the calculation method. Today we will talk about Digital Versatile Disc technology and understand the nuances of calculating the volume of such storage media.

Problem with definitions

The term DVD, surprisingly, does not have an unambiguous definition. This technology was developed to replace conventional compact discs (CDs), which were increasingly becoming insufficient in capacity. Originally, the abbreviation DVD stood for Digital Video Disc. However, it later became clear that it was possible to record not only movies, but also other files.

This was the reason that some began to put a different meaning on the term, understanding DVD as a Digital Versatile Disc. In general, both transcripts are correct.

Increasing available volume

It was previously indicated that DVDs have replaced CDs, the capacity of which has become insufficient. In order to read the digital data recorded on the surface, it is necessary to use a thin laser beam. For this purpose, disk drive devices implement a special unit consisting of a emitting element and a focusing system. The main difference between the beam of light used to read and write information is that it is coherent, that is, it is very narrowly focused. This makes it possible to practically eliminate the effects of diffraction and interference of light waves. When the CD standard was developed, the miniature semiconductor emitters available at that time were unable to create a sufficiently narrow beam, so the width of the track on the metal base of the disc was about 1.6 microns. Subsequently, more advanced light-emitting diodes were developed, the beam of which was so thin that the width of the track could be halved. Thus, it became several times higher than the same parameter CD. In addition to the width of the track, it was possible to change the distance between them, as well as the size of the pits.

"Pie" from disks

The capacity of a DVD disc is determined not only by the above dimensions and the configuration of the laser beam. Those were created that, in fact, combined several disks at once in one product while maintaining standard dimensions.

Such multilayer compacts can be compared to a sandwich. During production, not one, but two tracks are used at once, but located in such a way that the reading laser beam passes freely through the translucent upper surface. Their volume reached 8.54 GB. The maximum capacity of a DVD disc whose diameter is not 12, but 8 cm is 5.32 GB. Structurally, the drive can have two emitters, each of which focuses on its own depth (surface). There are models with a single beam, the focusing of which is controlled electronically. The information capacity of DVDs could be even greater when so-called double-sided solutions were used. Outwardly, it is an ordinary compact, but writing/reading is possible on both sides, which in most drives required turning the media over. The capacity of a DVD disc of this modification ranges from 9.4 GB (double-sided single-layer) to 17.08 GB (four layers, recording on both sides). However, such “pies” were not widely used due to the higher cost of production and the need to handle them too carefully, since the slightest scratch could lead to the inability to read data from deep layers.

Saving information

RAM disks are based on the technology of heating the surface with a laser beam. Their feature is the ability to perform formatting to the usual and selective deletion of files. Structurally, such disks are located in special cartridges, which increases their reliability. Theoretically, if you remove DVD-RAM from the case, you can work with it on a drive designated as Multi. These are quite reliable solutions.

The information capacity of this type of DVD ranges from 1.46 GB (single-layer, single-sided, 8 cm) to 9.4 GB (double-sided). The term RAM means that rewriting is physically possible. The abbreviation can be translated as “Random Access Memory”. In fact, this type of disk is intended for data backup and was an excellent solution before the advent of alternative media. Especially when you consider the stated duration of data storage (about 30 years) and the number of rewrite cycles (more than 100 thousand). The disadvantage is the relatively high cost and low distribution.

Video compacts

The next solutions are DVD-Video. Such discs are designed for recording a multimedia stream. Designated as “DVD-1…18”. The first four are modifications with a reduced diameter (8 cm versus standard 12). DVD-5 is considered a classic, from which you can read 4.7 GB (single-layer, single-sided).

Accordingly, the maximum DVD capacity in this category is 17.08 GB (DVD-18, two sides, four layers). Since mass-produced video players use the simplest focusing units, which reduces the cost of production, not all models are capable of reading large-capacity discs. The exception is single-layer double-sided ones, to work with which you just need to turn the disk over in the drive. Their disadvantage is that there is no space for a label, so the name is indicated on the transparent part, next to the central hole.

Write once

The advent of disk drives capable of recording digital data on discs at home has made a real revolution in the field of backup and the creation of real film libraries. DVD+-Rs are initially sold without recording. The owner of a special drive can save any information converted into digital form on such a disk.

The color is mirror blue, with a tint in the violet region of the spectrum. The capacity of this type of DVD ranges from 4.7 GB (one layer on one side) to 17.08 GB. The volume depends, as usual, on the number of layers and sides. But still, because of the correct one, the simplest 4.7 GB compacts are most widely used. Previously, recording could only be done using a computer disk drive, but now many video players that can save TV programs to disks have this ability. The problem of compatibility of “-” and “+” R has long been a thing of the past and is not discussed in the article.

Multiple write

The disadvantage of the previous type of disk is obvious - they cannot be re-written by deleting the data. To solve this issue, fundamentally different discs were proposed, called DVD+-RW. They can be used almost like a regular drive. The term RW means Rewritable, i.e. rewritable. The capacity of DVDs of this class is exactly the same as that of “simple” R ones. However, double-layer ones are extremely rare due to the need to purchase a special drive capable of working with such discs.

In addition, rewritable solutions already require careful handling, and the complexity of their design means that you actually have to blow dust off such disks. And an accidental scratch on the surface may not allow reading information from the lower layers. Thus, a “classic” is a single-layer, single-sided disc. The surface color varies from gray to almost black. The number of rewrite cycles is officially about several thousand, but in practice such a disc can be written no more than 50-100 times. And then over time, the reliability of data storage decreases. Thus, DVD-RWs are suitable for short-term data storage and transfer. Writing can be done in blocks as usual. At the same time, using the Windows mechanism, it is also possible to work as with a regular drive (reading/writing arbitrary files). However, due to the fact that the standard of rewritable discs does not allow high speeds, you usually have to be content with four times, equal to 5.5 MB.

Recording feature

Standard DVD capacity may be slightly exceeded. This is achieved through the use of the lead-out zone. The Overburn function must be supported by the device itself. It can be activated in the popular Nero program by going to “Options - Expert Properties”. We do not recommend using this feature without it, as you may be unable to read such a disc on a drive that cannot work with Overburn.

How is volume calculated?

Many computer owners have long noticed that it is impossible to burn onto a CD what is specified by the manufacturer. In fact, there is no deception here. It’s just that disk manufacturers, for marketing reasons, believe that there are 1000 bytes in 1 KB, although in reality there are 1024 (raising two to the tenth power). With increasing volume, this number grows progressively. Consequently, no more than an “honest” 4.38 GB fits on a standard DVD.