Файл: Modern multimedia technologies.pdf

Video and animation. Now, when the scope of personal computers is expanding, there is an idea to create a home video Studio based on a computer. However, when working with a digital video signal, you need to process and store very large amounts of information, for example, one minute of a digital video signal with SIF resolution (compatible with VHS) and true color rendering (millions of colors).

(288 x 358) pixels x 24 bits x 25 frames / s x 60 c = 442 MB,

in other words, it is not possible to save a full-time video recorded in this format on media used in modern PCs, such as a CD-ROM (about 650 MB) or a hard disk (several gigabytes). Using MPEG compression, the volume of video information can be reduced without noticeable image degradation. What is MPEG?

MPEG is an acronym for Moving Picture Experts Group. This expert group works under the joint leadership of two organizations - ISO (international standards Organization) and IEC (international electrotechnical Commission). The official name of the group is ISO/IEC JTC1 SC29 WG11. Its task is to develop common standards for encoding audio and video signals. MPEG standards are used in CD-i and CD-Video technologies, are part of the DVD standard, and are actively used in digital radio broadcasting, cable and satellite TV, Internet radio, multimedia computer products, ISDN communications, and many other electronic information systems. The abbreviation MPEG is often used to refer to standards developed by this group. To date, the following are known:

MPEG-1 is designed for recording synchronized video images (usually in SIF format, 288 x 358) and audio on a CD-ROM with a maximum reading speed of about 1.5 Mbit/s.

The quality parameters of video data processed by MPEG-1 are in many ways similar to normal VHS video, so this format is used primarily where it is inconvenient or impractical to use standard analog video carriers.

MPEG-2 is designed for processing video images of comparable quality with television at the bandwidth of the data transmission system in the range of 3 to 15 Mbit / s, and professionals use the best streams. hardware uses streams up to 50 Mbit/s. Many TV channels are switching to technologies based on MPEG-2. the signal compressed in accordance with this standard is transmitted via television satellites and is used for archiving large volumes of video material.

MPEG-3-intended for use in high-definition television systems (high-definition television, HDTV) with a data stream speed of 20-40 Mbit/s, but later became part of the MPEG-2 standard and is no longer separately mentioned. By the way, the MP3 format, which is sometimes confused with MPEG-3, is intended only for audio compression and the full name of MP3 sounds like MPEG Audio Layer III

MPEG-4-defines the principles for working with digital representation of media data for three areas: interactive multimedia (including products distributed on optical disks and over the Network), graphic applications (synthetic content), and digital television.

How does compression work? The basic encoding object in the MPEG standard is a frame of a television image. Since the background of the image remains fairly stable in most fragments, and the action takes place only in the foreground, compression begins with the creation of the original frame. Source (Intra) frames are encoded only using intra-frame compression using algorithms similar to those used in JPEG . The frame is divided into blocks of 8x8 pixels. A discrete-cosine transformation (DCP) is performed over each block, followed by quantization of the obtained coefficients. Due to the high spatial brightness corellation between neighboring pixels of the image, DCP leads to the concentration of the signal in the low-frequency part of the spectrum, which after quantization is effectively compressed using variable-length encoding codes. Predicted frames are processed using forward predictions based on previous source or predictable frames.

The frame is divided into macro blocks of 16x16 pixels. each macro block is assigned the most similar section of the image from the reference frame, shifted by the displacement vector. This procedure is called motion analysis and compensation.

The acceptable compression ratio for predictable frames is 3 times higher than for original frames. Depending on the nature of the video image, bi-directional interpolated frames are encoded in one of four ways: forward prediction; reverse prediction with motion compensation - used when new image objects appear in the encoded frame; bidirectional prediction with motion compensation; intra - frame prediction-when the plot changes abruptly or when the image elements move at a high speed. Bidirectional frames are associated with the deepest compression of video data, but because a high compression rate reduces the accuracy of restoring the original image, bidirectional frames are not used as reference frames. If the DCP coefficients were transmitted accurately, the restored image would completely match the original one. However, errors in the recovery of DCP coefficients associated with quantization lead to image distortion.

The coarser the kvntovanie, the smaller the volume occupied by the coefficients and the stronger the compression of the signal, but also the more visual distortion.

SOUND. Digital recording, editing, working with wave forms of audio data, as well as background playback of digital music is possible (Fig. 8). work via MIDI ports is Provided. The Converter mentioned above also converts audio data between WAVE, PCM, and AIFF formats (Apple audio file format). Recently, the Mp3 format has become particularly popular. It is based on MPEG-1 Layer III (this is the part of the standard we are talking about) based on the features of human auditory perception, reflected in the "pseudo-acoustic" model. MPEG developers proceeded from the postulate that not all the information contained in the audio signal is useful and necessary - most listeners do not perceive it. Therefore, some of the data may be considered redundant. This "extra" information is deleted without much harm to the subjective perception. The acceptable degree of "cleaning" was determined by repeated expert auditions. This standard allows to set limits to change the encoding settings to get less compression with the best quality, or conversely, to go on the loss of perception for a higher compression ratio. An audio wav file converted to MPEG-1 Layer III format with a bitrate of 128 Kbytes/sec takes up 10-12 times less space on the hard drive. A 100-megabyte ZIP diskette can hold about an hour and a half of sound, while a CD can hold about 10 hours. When encoding at a speed of 256 Kbytes / sec, about 6 hours of music can be recorded on a CD with a difference in quality compared to a CD, accessible only to a trained expert ear.

TEXT. In the Microsoft guide, special attention is paid to the means of entering and processing large arrays of text. We recommend various methods and programs for converting text documents between different storage formats, taking into account the structure of documents, control codes of text processors or typesetting machines, links, tables of contents, hyperlinks, etc., inherent in the source document. You can also work with scanned texts and use optical character recognition tools.

The Multimedia Development Kit (MDK) developer package includes tools (programs) for preparing multimedia data BitEdit, PalEdit, WaveEdit, FileWalk, as well as MSDK libraries of the C language for working with data structures and multimedia devices, extensions of the Windows 3.0 SDK.

Among the author's tools recommended for MOS are Schoolbook, Guide, and Authorware Professional.

Multimedia Windows architecture provides device independence and extensibility. The upper system level of translation, represented by the MMsystem module, isolates user programs (application level) from device-specific drivers.

MMsystem includes Media Control Interface (MCI) tools that control video recorders, video disks, audio CDs, and work with scanners, digitizers, and other devices. To do this, they turn to the MCI drivers that provide the upper level of control. MCI drivers, after processing the request, access the devices, as well as MEDIAMAN (Media Element Manager). MEDIAMAN manages I / o handlers for bitmap files and audio WAVE files. MMsystem also includes lower-level programs Low-Level Functions that control drivers of audio and WAVE devices, MIDI, and joysticks.

The necessary drivers are connected at the execution stage. Contacting drivers is based on the principles of sending messages, which simplifies and unifies their writing and working with them.

To represent multimedia data, the RIFF file structure (Resourse Interchange File Formal) has been developed, which should provide uniform rules for recording and playing multimedia data, data exchange between applications, and in the future - between different platforms.

In General, Multimedia Windows tools are designed with an interface, although somewhat heavy, devoid of elegance, lightness, for the user. In the near future, with the advent of new tools created specifically for this architecture or ported from other platforms, with the overcoming of the VGA resolution barrier, the Multimedia Windows environment will be quite "true multimedia" - a system of "true multimedia". Already there are applications for this environment that use methods of software compression of information and play video-up to 15 frames / s in a small window on the screen (Fig. 9). Microsoft developed its own software compression tools, Audio-Video Interieaved (AVI), which it released in the second half of 1992.

The Microsoft Windows 3.1 operating environment, which comes with multimedia systems, integrates many properties of Multimedia Windows, and provides standard support for CD-ROM players. In 1992-93, the MPC consortium switched to multimedia systems based on IBM PC AT 486 personal computers with high-speed CD-ROM (MPC Level 2). The main requirement for a multimedia system that meets the second level is the ability to play a digital video in a 320 * 40-point window at a speed of 15 frames / s, as well as the presence of a video adapter that provides at least 65,000 color shades.

6) Multimedia hardware

To build a multimedia system, additional hardware support is required: analog-to-digital and digital-to-analog converters for converting analog audio and video signals to a digital equivalent and back, video processors for converting conventional television signals to the form reproduced by the cathode ray tube display, decoders for mutual conversion of television standards, special integrated circuits for compressing data into files of acceptable sizes, and so on. All equipment responsible for sound is combined into so-called sound cards, and for video into video cards. Further details are discussed separately about the device and characteristics of sound cards, video cards and CD-ROM drives.

7) Sound card

Over time, the list of tasks performed on the PC went beyond just using spreadsheets or text editors. CDs with audio files, preparing multimedia presentations, holding video conferences and telephone facilities, as well as playing games and listening to audio CDS all this requires that sound become an integral part of the PC. This requires a sound card. Game lovers will be satisfied with the new surround sound features.

The following trends are observed for IBM compatible computer sound cards:

First, instead of frequency modulation (FM), more and more people use wavetable or wt Synthesis to play sound. The signal received in this way is more similar to the sound of real instruments than with FM Synthesis. Using the appropriate algorithms, even just one tone of a musical instrument can reproduce everything else, that is, restore its full sound. Samples of such signals are stored either in the device's permanent memory (ROM), or programmatically loaded into the sound card's RAM.

In cheaper boards, frequency modulated synthesis using sinusoidal vibrations is more often implemented, which leads to an imperfect sound of instruments, the reflection of sound and roar characteristic of the latest generation of games in gaming halls. A wave synthesis chip located on the Board stores pre-recorded digitized samples of the sound of musical instruments and sound effects. The results are obvious, the music recordings are more convincing, and the gamblers are more impressionable.

Ensoning became a pioneer in the implementation of Wtsynthesis in 1984. Soon Wtsynthesizers were produced by such well-known companies as Emu, Korg, Roland and Yamaha.

Companies that produce sound cards add wtsynthesis in two ways, either by embedding it on the sound card as chips, or by implementing It as a child Board. In the second case, the sound card is cheaper, but the total cost of the main and child boards is higher.

Second, it is compatible with sound cards. For a relatively short history of multimedia development, several basic de facto standards for sound cards have already appeared. So almost all sound cards designed for games and entertainment support compatibility with Adlib and Sound Blaster. All business - oriented sound cards are usually compatible with Microsoft's MS Windows Sound System.

Third, one of the components of modern sound cards has become a signal processor DSP (Digital Signal Processor). the main functional responsibilities of this device include: speech recognition, three-dimensional sound, Wtsynthesis, compression and decompression of audio signals. The number of sound cards equipped with DSP is not so large. The reason for this is that such a powerful device helps only when solving strictly defined tasks.

As a rule, a DSP device is quite expensive, so it can only be installed on professional music cards right away. One of the most powerful DSP manufacturers is now Texas Instruments.

Fourth, there is a steady trend of integrating the functions of sound cards on the system Board. Despite the fact that a number of manufacturers of motherboards already include microchips for audio reproduction in their products, concerns are not noticeable in the ranks of suppliers of sound cards.

A potential problem when using built-in audio processing tools is the limited system resources of IBM PC compatible computers, namely the possibility of conflicts over direct memory access (DMA) channels. An example of such a Board is the OPTi495 SLC system Board, which uses a 16-bit AD 1848 audio stereo codec from ANALOG DEVICES.

Fifth, the desire for more natural sound reproduction forces manufacturers to use three-dimensional or three-dimensional (3D) sound technologies.

The most fashionable direction in the field of sound reproduction these days provides the so-called surround sound. The use of these surround sound effects allows you to expand the stereo space which in turn gives greater depth to the limited field of reproduction inherent in not large closely spaced speakers.

Sixth, it is the connection of CD-ROM drives. Almost all sound cards have built-in interfaces for connecting CD-ROM drives of one or all three companies Sony, Panasonic/Matsushita and Mitsumi. However, most sound cards are designed to connect Sony drives.

There are cards and drives that support the standard ATA interface (IDE), used for computers with a hard drive.

Seventh, the cards use Dual DMA mode, i.e. double direct access to memory. Using two DMA channels, you can realize simultaneous recording and playback.

And the last is the steady introduction of sound technologies in telecommunications.

Sound cards are purchased in 90% of cases for games, of the remaining 10% for speech accompaniment of multimedia programs. In this case, the consumer quality depends only on the DAC (digital-analog Converter) and the audio frequency amplifier. Even more important is compatibility with the Sound Blaster standard, since not all programs will support less common standards.

The set of Sound cards includes drivers, utilities, programs for recording and playing sound, tools for preparing and producing presentations, encyclopedias, and games.

8) Laser disks, CD-ROM

Due to the growing volume and complexity of software, and the widespread introduction of multimedia applications that combine moving images, text, and sound, CD - ROM readers have recently become extremely popular. These devices and the disks themselves are relatively inexpensive, very reliable, and can store very large amounts of information (up to 650 MB), so they are very convenient for delivering more programs and data, such as catalogs, encyclopedias, as well as training, demonstration, and game programs. And many programs are fully or partially delivered on CD-ROM.

History of development. Compact discs originally designed for fans of high-quality sound, firmly entered the market of computer devices. Optical CDs were replaced by vinyl in 1982. It was decided that the standard is designed for 74 minutes of "Red Book"sound. When 74 minutes were converted to bytes, it turned out to be 640 MB.

The first drives had a single speed of 150 KB/s. Models of drives with double speed appeared in 1992. Drives with tripled and quadrupled speed in early 1994. Today we are talking about a speed increased by six or even eight times. The speed increase coefficient is not necessarily a whole one.

Principle of operation. As in CDs used in household CD players, information on computer CDs is encoded by alternating between reflective and non-reflective areas on the disk substrate. In the industrial production of compact discs, this substrate is made of aluminum, and the areas that do not reflect light are made by pushing holes in the substrate with a special presform. In a single production of compact discs (so-called CD-R discs, see below), the substrate is made of gold, and information is applied to it by a laser beam. In any case, there is a transparent coating on top of the CD-ROM backing that protects the information stored on the CD from damage.

Although the appearance and size of CDs used in computers do not differ from those used in household CD players, however, computer devices for reading CDs are significantly more expensive. This is not surprising, because reading programs and computer data should be performed with much higher reliability than is sufficient when playing music. Therefore, the reading used in the computer's CD-ROM drive is carried out using a laser beam of low power. Using this technology allows you to write a very large amount of information (650 MB) to CD-ROMs, and provides high reliability of information.

However, the speed of reading data from CD-ROMs is significantly lower than from hard disks. One of the reasons for this is that CD-ROMs do not rotate at a constant angular speed when reading, but rather in such a way as to ensure a constant linear rate of departure of information under the reading head. The standard speed of reading data from CD-ROMs is only 150-200 KB / s, and the access time is 0, 4 s. However, in recent years, mainly devices with double, triple and even fourth rotation speeds are produced, they provide correspondingly higher speed indicators: access time 0, 2-0, 3 seconds, reading speed 500 Kbytes/s. Note, however, that devices with triple speed in real-world tasks do not increase the speed of working with a CD by one and a half or two times compared to a device with double speed, but only by 30 to 60%.

9) Video card

There are a large number of devices designed to work with video signals on IBM PC compatible computers. It can be divided into several groups: devices for entering and capturing video sequences (Cupture play), framegrabbers (Framegrabber), TV tuners, vgatv signal converters, and MPEG players.

TV-tuners:

These devices are usually made in the form of cards or a box (a small box). They convert an analog video signal coming over a cable TV network or from an antenna, a video recorder, or a camcorder. TV tuners can be part of other devices such as MPEG players or frame grabbers.

Some of them have built-in audio conversion chips. A number of tuners have the ability to output Teletext.

The frame grabbers:

They appeared about 6 years ago. As a rule, they combine graphics, analog-digital and video processing chips that allow you to sample the video signal, save individual image frames in a buffer and then write them to disk, or output them directly to a window on a computer monitor. The contents of the buffer is updated every 40 MS. that is, with the frame rate. Video signals are output in overlay mode (overby). To implement a window on the monitor screen with live video, the frame grabber card is connected to the graphics adapter via a 26-pin Feature connector. It usually comes with a Video fjr package that outputs images of 240*160 pixels when playing 256 colors or more. The first devices are Video Blaster, Video Spigot.

VGA-TV converters:

These devices transmit a signal in a digital image of a VGA image to an analog signal suitable for input to a television receiver. Manufacturers usually offer such devices made either as an internal ISA card or as an external unit.

A number of converters allow you to overlay a video signal for example to create titles. In this case, the converted computer signal is fully synchronized via external (gtnlok). When overlaying, a special key signal of three types is formed: lumakey, chromakey, or alpha chenol.

1.in the first case, the overlay is made where the brightness Y exceeds the specified level.

2. The superimposition image is transparent only where its color matches with the set.

3. alpha channel is used in professional equipment based on the formation of a special signal with a simple distribution, which determines the degree of displacement of the video image at various points.

MPEG players:

These devices allow you to play sequences of video images (movies) recorded on CD-ROMs with VNS quality, the speed of compressed information flow does not usually exceed 150 KB/s.

The main difficulty of the problem solved by the MPEG encoder is to determine the optimal correlation between three types of images for each specific video stream: (I)ntra, (P)redicated, and (B)idirectional. The first MPEG players were the sigina Desing Reel Magic Board in 1993.

10) Conclusion

Multimedia technologies are constantly developing and moving forward. If floppy disks were popular and breakthrough before, now they seem useless and weak compared to other modern devices.

11) List of references

1. https://ru.wikipedia.org/wiki/Мультимедиа
2. https://moluch.ru/archive/258/59184/
3. https://cyberleninka.ru/article/n/sovremennye-multimediynye-tehnologii-i-sredstva-v-organizatsionnyh-sistemah-1