>>Informatics: Technical multimedia tools

§ 25. Multimedia technical means

Main topics of the paragraph:

Sound input/output system;
devices for working with video frames;
multimedia storage devices.

Multimedia storage devices

Sound, video, graphics combined into a multimedia application require large amounts of memory. Therefore, to store them you need sufficiently capacious and, preferably, inexpensive media. These requirements are met by optical compact discs (CD - Compact Disk). Along with their large capacity (about 700 MB), they have reliable protection against data loss. Currently, CD-ROM and CD-RW disks are widely used (see § 8). Digital video discs - DVDs - have the greatest information capacity. A modern DVD can store up to 20 GB information. This is enough to host a full-length movie with high-quality sound.

Briefly about the main thing

To work with sound, a microphone is used, sound card and speakers (speakers or headphones).

Analog video recording must be digitized before processing on a computer.

To store multimedia applications, CDs containing large amounts of information are used.

DVDs are designed to store full-length video films with high-quality audio.

Questions and tasks

1. What elements of a sound card are responsible for playing digital and synthesized sound?
2. Why are CDs used to store multimedia applications?
3. Why are special input/output cards used for working with video?
4. For what purposes is a multimedia projector used?

I. Semakin, L. Zalogova, S. Rusakov, L. Shestakova, Computer Science, 8th grade
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The source of the video signal is most often an analog device - a television tuner, VCR, video camera. To transmit digital video (for example, a signal from digital video cameras) to a computer, a special digital FireWire port is used. However, digital video cameras have not yet become widespread. Therefore, for computer processing of signals from analog video devices, it is necessary to digitize them, that is, convert them from analog to digital form. This requires I/O cards to take the incoming analog video signal and digitize it in real time, which then needs to be stored on the hard drive. After saving the digitized image, it is edited. These functions are performed by the video signal capture device.

A video capture device - a video blaster (VideoBlaster) is a video card, also called an image grabber, a video input device, a TV grabber (Grab), image capturers (Image Capture), and provides:

Reception of low-frequency video signal (from a video camera, tape recorder or television tuner) to one of the software-selectable video inputs;

Display received video in real time in a scalable window in the Windows environment (a VGA monitor can be used instead of a TV);

Freezing a frame of digitized video;

Saving the captured frame on a hard drive or other accessible storage device as a file in one of the accepted graphics standards (TIP, TGA, PCX, GIF, etc.).

A generalized diagram of a device of this type is shown in Fig. 4.22.

The video decoder provides reception of a signal from one of the inputs, its digitization, digital decoding according to the television standard and transmission of the received YUV data to the video controller.

The video controller organizes streams of digitized data between the elements of the video card, carries out the necessary digital conversions of data (for example, YUV to RGB, scaling), organizes their storage in a buffer of its own memory, transfers data via the computer bus when saving it on the hard drive, and also transfers it to a digital-to-analog converter.

The digital-to-analog converter, together with the video controller, participates in the formation of a “live” TV window on the monitor screen, performs reverse analog conversion of the digital captured image, and transmits a signal from the video adapter or an RGB signal from the memory buffer to the monitor.

When choosing a video blaster card, you need to take into account its main indicators:

frame resolution in the saved video stream;

possibility and types of hardware compression (compression) of video information in real time;

possibility of simultaneous input of video and audio information. N

The most common video blaster cards are:

mass cards entry level;

semi-professional;

entry-level professional cards;

professional.

Entry-level mass cards capable of capturing and storing a video stream on a hard drive with a frame resolution not exceeding 352 x 288 pixels, although twice the resolution is possible for saving individual frames. There is no hardware video compression, so when working with such cards it is necessary to use a special program - an encoder, which allows you to compress the video stream in real time using the MPEG-1 or MPEG-2 algorithm. There is no sound input in devices of this class, which requires separate sound recording through the sound card input.

Semi-professional cards provide a resolution of 768 x 575 pixels, corresponding to the standard for video in PAL format; support the simplest type of hardware video compression, M-JPEG, which allows you to reduce the volume occupied by a digitized film by 100 times. However, these cards do not have a sound input.

Entry-level professional cards have an audio input, which allows you to simultaneously record on HDD video and sound accompaniment; provide hardware compression of the M-JPEG type and can be used not only for input, but also for outputting an edited video from a PC to a VCR. The latter allows you to store films on a regular video cassette when using a computer as an editing table.

Professional cards have the ability to hardware compression using the MPEG-1 or MPEG-2 algorithm, reducing the volume of the digitized film by 200 times.

After editing and editing, the video can be re-recorded onto an analog video cassette using the video input of the same card, or subjected to even more stringent compression using the MPEG-4 algorithm for subsequent recording on CD-R.

In order to transfer video recordings (analog or digital) to a computer and then burn them to a CD or DVD, you will need a special video capture card (otherwise the video image from the magnetic tape will not be able to get into the computer).

If you have a modern digital camera, then the problem can be solved simply: to input video into your computer you will need an inexpensive IEEE-1394 (FireWire) interface card, unless, of course, your computer or laptop is immediately equipped with such an interface (many modern laptops And motherboards manufactured with a built-in IEEE-1394 controller).

In principle, you can buy any such board (prices range from $25 to $50), but make sure that the kit includes a cable with a small 4-pin connector (that is, without power) that you will use to connect this board to the digital camera (such cables are usually not included with the camera). However, the cost of such a cable, if purchased separately, today does not exceed $10. Please note that the types of cables and connectors on the IEEE-1394 board are different. They can have either 4- or 6-pin connectors or combinations of both. It is better to have two types of connectors on the board at once (so that you can connect various FireWire devices in the future), but for working with video, a 4x4 pin cable is preferable. Then you can use the same cord to transfer video from camera to camera, bypassing the computer.

The board may be the simplest and cheapest; if its installation went without problems and it worked normally, then it will continue to work no worse than the expensive one. After this, almost any modern video editing program will cope with the task - it will enter video and sound into the computer, edit them and prepare them for recording on a CD or DVD.

Owners of old analog cameras or video recordings will be somewhat disappointed - the prices for decent analog video capture cards are significantly higher (from $150 without software) and also depend on such parameters as the possibility of encoding and the resolution of the resulting frame. In principle, to digitize a low-quality analog signal, you can use the video input of a standard computer video card (if the latter is equipped with the VIVO - Video In/Video Out option) or the video input of a TV tuner, but in this case you will get unsatisfactory signal quality, which will deteriorate even more after application of MPEG compression. Do not believe manufacturers' statements that compare the quality of such cards or TV tuners with analog video and claim that the quality of digitization corresponds to the VHS standard. The defects in a compressed digital image are different from those in an analog image, even if the analog video is played back from an unsightly home VCR. And if you “ruin” the video during capture and digitization, then compression in MPEG will greatly aggravate the analog flaws and add its own digital artifacts.

In addition, standard monitor video cards and tuners, as a rule, do not capture the full frame; when working with them, frame skips are possible, and when processing the resulting image, it is encoded in digital format has to be done programmatically, which reduces quality and requires additional time. In addition, such devices have difficulties synchronizing audio and video.

A full-fledged modern analog video capture card simultaneously digitizes both video and audio signals, and some cards immediately compress the input image using a specific algorithm (M-JPEG, DV, and sometimes MPEG-1 or MPEG-2), which speeds up data transfer to a computer, saves disk space and makes it easier further work with the film. Obviously, the lower the compression ratio that such cards can provide, the higher the quality of the video material, but the more expensive they are. In addition to high-quality digitization, specialized video capture cards have the ability to render special effects and transitions in hardware, which reduces the load on the system as a whole and reduces the wait when rendering the final film.

In addition to boards, there are external hardware converters (Fig. 1). As a rule, these are DV converters that convert an analog signal to DV format, but the reverse operation can be done. These devices reduce the load on the computer, do not occupy a PCI slot, and allow you to convert analog recordings to digital form (and vice versa). They connect to conventional IEEE-1394 or USB controllers and have a patch panel with analog inputs and outputs for connecting household devices. They cost about $300, and are convenient to use if you temporarily have an analog video camera and need to edit the captured image until you purchase a camera in one of the digital formats.

There are also hardware converters to MPEG-1 or MPEG-2. Such devices are connected to the computer via a USB interface (note that in this case the computer must have USB interface 2.0, since the 1.1 standard allows you to work only with very low flow, and the higher the maximum throughput of the converter, the best quality will have the input video material).

With this capture, it is also possible to correct video parameters (brightness, contrast, color) and sound (level, balance), and the resulting file can be immediately recorded on DVD video, which significantly saves the time usually spent on software rendering. Such devices cost, depending on the quality of the codec, from $200 and above.

In fact, there are not so many similar boards and external converters produced - perhaps there are only a dozen in the whole world. Such solutions are traditionally offered by Matrox, Pinnacle, Canopus and Dazzle, and now, perhaps, they are also produced by little-known companies, information about which has not yet reached us. Decent boards with software codecs cost about $400 in RTL kits (that is, with software).

Let's consider such solutions using the example of Canopus Let's EDIT RT+ (this is a PCI card for real-time video editing, which has a certain versatility - in addition to analog inputs and outputs RCA/S-Video in/out, it has digital interface IEEE-1394). Video encoding/decoding is carried out by a computer, but some special effects are calculated in real time.

Let's also mention a more complex board for video capture and editing from the same manufacturer - Canopus DV Storm SE (S-VHS/DV/ IEEE-1394), but it already has a hardware codec, so compositing and all 2D and 3D effects are performed in real time, but also costs significantly more - under a thousand dollars.

Canopus Let's EDIT RT+

Lata Canopus Let’s EDIT RT+ (Fig. 2) is positioned by Canopus as a solution for editing digital video in real time. Its cost together with the software is about $400 (however, the Canopus Let’s EDIT program, sold separately for editing DV video, costs about $150).

Canopus Let's EDIT RT+ has an IEEE-1394 digital interface, analog inputs and outputs for composite video (RCA tulips), S-Video inputs and outputs, as well as jacks for connecting an audio signal. There is another option, Canopus Let’s EDIT RT (without plus), which, unlike the previous one, does not have analog outputs (only inputs), but costs about $100 less. Please note that if you subtract the cost of the software from the price, then the latter option will cost $150, just like simpler video capture cards.

Let's Edit this is very simple program entry-level video editing with real-time processing and effects. The program was developed on the basis of the Canopus Edit line of programs that came with mid-price video editing boards. Let's Edit can work with any FireWire controllers. The program allows you to create multi-track projects with 2D/3D effects and filters, has two tracks for video, five tracks for titles and four tracks for audio. In addition, Let's Edit has built-in tools for color correction and changing playback speed. MPEG-1, MPEG-2, Real Media, Quicktime and Windows Media can be used as output formats for saving the result.

	Useful programs in the Internet After capturing (digitizing) the video image, the most painstaking work of editing and editing the video begins. One of the most common video editing programs is considered Adobe Premiere, but other packages such as Ulead Media Studio Pro and Pinnacle Edition are no less functional. You can also note the completely Russified (and officially) Pinnacle Studio program, which recently released its 9th version. However, do not forget the simplest, freely distributed program for capturing and editing video VirtualDub (http://www.virtualdub.org), as well as a special restoration filter for VirtualDub (also free), which will allow you to restore video, especially damaged in as a result of storage on outdated analog media.

The Canopus Let's EDIT RT family of products can be considered as an alternative to Pinnacle's junior products with Pinnacle Studio software (which were once sold under the Miro brand and were widely known to video enthusiasts).

Minimum system requirements to Canopus Let’s EDIT RT boards are quite low: an Intel Pentium III 800 MHz processor or AMD Athlon 800 MHz; 256 MB RAM; Windows 2000 with SP3 or XP with SP1; boards are inserted into the slot PCI version 2.1 or higher; The video card requires support for DirectDraw overlay; color depth of at least 24 bits; monitor resolution 1024S768; The hard drive should provide a data transfer speed of about 10 MB/s. You may also need an additional sound card to record voice comments (remember that these boards support sound independently - two channels of 48/44.1/32 kHz, 16 bits).

However, for more efficient work Canopus recommends using Intel processors Pentium 4 with clock frequency from 2 GHz or AMD Athlon from 2 GHz (it is claimed that multiprocessor systems and Hyper-Threading technology are supported, although we did not find much difference in performance). Naturally, for comfortable work with video, it is also better to increase the memory volume to at least 512 MB.

The following connectors are located on the boards: bidirectional (input-output) i-Link, also known as IEEE-1394 (four pins), bidirectional IEEE-1394 (six pins). The RT version also has an S-Video/RCA input and a stereo audio input (RCA tulips). The RT+ version, in addition to inputs, also has S-Video/RCA outputs, as well as a stereo 3.5 mm Phono mini-jack input-output (an adapter from minijack to RCA tulips is included in the kit).

In addition to the board itself, the kit includes software (Let's Edit and Ulead DVD Movie Factory), a FireWire cable (4-4), an RCA to S-Video adapter (RT+ has two of them - a 7-pin combined miniDIN compatible with S-Video , and RCA-composite), and also, as we have already said, RT+ additionally provides phono-RCA adapters.

Both boards support PAL or NTSC video standards (they are switchable on the board), resolutions up to 720×576, frame rates - 25 frames per second for PAL and 29.9 for NTSC. Sound standards - PCM, Wave. It is claimed that the boards have hardware support for 2D and 3D effects, which speeds up the rendering of the final image.

As for the Canopus Let's EDIT RT board (without a plus), its fate is unenviable - buying for $300 a solution without analog outputs that would allow you to control the editing process, for example, on a regular TV, and even with such an inconvenient editing program as Let's Edit seems dubious to us. It is the analog output of Canopus Let’s EDIT RT+ (according to the documentation, the board is called ACEDVio) that turns this solution into a full-fledged editing complex with the ability to bidirectionally convert analog video to digital (and vice versa), as well as edit the resulting video in real time with constant monitoring on a large TV screen. Canopus Let's EDIT RT+ is perhaps one of the few solutions in this price category that has an analog output for the DV format.

However, this way you can only work with the original ACEDVio codec in the Let’s Edit editor, and when you switch to another editor, for example in Adobe Premiere, you will need to recalculate and you will no longer be able to display the edited video on your TV. In turn, when working with the Let’s Edit program, there is a file size limit of 2 GB, which is typical for all previous generation Video for Windows software codecs (this problem was solved only after the developers switched to the DirectShow standard). It turns out that it is impossible to digitize an analog video fragment longer than 10 minutes into DV format, which is not always convenient (especially since an analog source, unlike a DV camera, is not controlled by time code in any way and any positioning on the tape is done by eye). This situation is surprising for motherboards of this level. It was not possible to find out the reason for such a limitation for a board that actively uses DirectDraw (perhaps the Let’s Edit program is to blame). In other programs, this board works as a standard IEEE-1394 (FireWire) controller and such problems do not arise.

However, the quality of digitization is quite high (see Fig. 3), and if you are not bothered by the shortcomings of the Let’s Edit editor, then choosing the RT+ board (ACEDVio) as a universal solution (that is, for working with both analog and digital video) is completely justified.

Lesson topic: « ».

Lesson objectives: 1. Introduce children to the concepts of " digital audio", "ADC", "DAC", "microphone", "audio adapter".

3. Give students a general understanding of the principles of operation of a tape recorder, phonograph, etc.

4. develop the ability to create sound files using the “sound recording” program

5. Develop logical thinking and memory;

6. Cultivate interest in the subject, caring attitude towards

COMPUTER.

Equipment:Multimedia equipment, board, presentation, tasks for practical work, stereo headphones with microphone, tutorial.

Lesson plan:

Organizing time

1. D/Z check (frontal survey)

   Explanation of new material

   Summarizing

During the classes:

Organizing time.

Greeting students. Checking attendance.

Checking d/z

What is multimedia?

Name the areas of application of multimedia.

What is the difference between a multimedia educational program and an educational video?

What advantages do multimedia applications have in education over the traditional form of education?

Explanation of new material.

The topic of our lesson today: “ Analog and digital audio. Multimedia technical means ».

At the end In the 19th century, the famous American inventor Thomas Edison made a phonograph.

The principle of operation of a phonograph

Speech, music, or singing create sound vibrations that are transmitted to the recording needle of a phonograph. The needle, acting on the surface of the rotating wax roller, leaves on it a groove with varying depth - a sound track. When playing sound, the opposite process occurs: the movement of the reading needle along the audio track is accompanied by its vibrations at the same frequency. These vibrations are converted by the phonograph into audible sound.

Edison's phonograph is the first sound recording device in history.

In the middle In the 20th century, an electrophone appeared - an electrical analogue of a gramophone.

Analogue sound representation

The soundtrack of a phonograph record is an example of a continuous form of sound recording.

This form is called analog. In an electrophone, the oscillations of a needle moving along a sound track turn into a continuous electrical signal.

IN In the 20th century, the tape recorder was invented - a device for recording sound on magnetic tape. It also uses an analog form of audio storage. Only now soundtrack- this is not a mechanical “groove with pits”, but a line with continuously changing magnetization. Using a magnetic reading head, an alternating electrical signal is created, which is sounded by an acoustic system.

Sounds- air vibrations - in the microphone of the tape recorder turn into vibrations electric current. The current creates oscillations in the magnetic field, which are “imprinted” on the tape, which is coated with a thin layer of iron powder. This recording method is called analog: one type of vibration turns into another, similar one. The sound is reproduced in the same way, but only in reverse: the magnetized tape, moving, causes the appearance of an electric current, which, after amplification, enters the speakers and makes them sound.

Digital audio- representation of an analog audio signal in the form of a bit sequence that corresponds to the levels of electrical sound vibrations at certain time intervals. To convert sound into digital form, pulse code modulation or, less commonly, sigma-delta modulation is used. In addition to describing sound vibrations in digital form, the creation of special commands for automatic playback on electronic devices is also used. musical instruments, the clearest example of such technology is MIDI.

Sound is recorded through a microphone, which creates a continuous electrical signal, and played back through speakers, which also sound under the influence of a continuous electrical signal. How does the operation of these devices combine with discrete data in computer memory? There is a conversion of the analog form of sound representation into a discrete one and the reverse conversion. The first process is called analog-to-digital conversion(ADC), second - digital-to-analog conversion(DAC).

Microphone used to input sound into a computer. Continuous electrical vibrations coming from the microphone are converted into a numerical sequence. This work is performed by a device connected to the computer called audio adapter, or sound card.

Playback of sound recorded in computer memory also occurs using an audio adapter, which converts digitized sound into an analog electrical signal audio frequency, arriving at acoustic speakers or stereo headphones.

The flow of sound from the source through the microphone, ADC, processor, DAC, loudspeaker and back into sound

Recording and playing videos on a computer, as well as working with sound, involve DAC-ADC conversion. For these purposes there are special video input/output cards. Video frames digitized and stored in computer memory can be edited.

optical compact discs.

Sound, video, graphics combined into a multimedia application require large amounts of memory. Therefore, to store them you need sufficiently capacious and, preferably, inexpensive media. These requirements are satisfied optical compact discs. Digital video discs have the greatest information capacity.

Reinforcing new material (frontal survey)

What are the first devices for reproducing sound?

Define the concept of digital sound?

What are ADC and DAC

Give examples technical devices, in which sound is stored and reproduced in analog form.

In what technical systems Is the sound transmitted in analog form?

Why can the form of sound representation in a computer be called discrete and digital?

Why are CDs used to store multimedia applications?

Why are special I/O cards used for video processing?

For what purposes is a multimedia projector used?

Practical work on the computer

Procedure for recording sound using the Sound Recorder program

1. Make sure you have an audio input device, such as a microphone, connected to your computer.

2. Open the Sound Recorder component. To do this, click the Start button. In the search box, type Sound Recorder, and then select Sound Recorder from the list of results.

3. After launching the Sound recorder program, its working window appears on the screen containing a recording scale and several buttons reminiscent of the controls of a conventional tape recorder (Fig. 1). To record audio, you need to perform a number of preparatory steps. First of all, you need to determine the source of the sound. To do this, open the program window Volume control(Volume Control), on the taskbar. In the window that appears, check the boxes to disable all devices except the one you need, for example, a microphone. Next, you should return to working with the recording program and adjust the recording quality for the soundtrack.

So far, we have only considered the problem of capturing and saving individual TV frames. But in order to make a movie or video, digitization of a video fragment is necessary. A direct solution to the problem of inputting a video sequence is not yet possible. The fact is that a 768x576 frame in the YUV 4:2:2 representation takes up 864 KB (in RGB 8:8:8 - 1296 KB), respectively, in 1 s (25 frames) the volume of digitized data will be 21 MB (32 MB ), and to record one minute of video, you will need a hard drive with a capacity of at least 1 GB. Of course, the problem lies not only in the volume of incoming information, but also in the speed of its transmission (during recording) and reading (during playback). Unfortunately, the realistically achievable video recording/reading speed on modern hard drives is 2-4 MB/s, although in special systems the speed approaches 7 MB/s.

Thus, when digitizing a video fragment, there are two problems:

Communication speed

Reducing data flow

The first problem is solved by developing new high-speed data storage devices. The second is difficult to solve using the following techniques:

Reducing frame size to 160x120 and number of colors to 256

Reducing the frame rate to 6--12 frames/s

Using video compression

The first two are the most obvious, but lead to a sharp deterioration in the visual quality of the video. The last method is the most effective.

A video blaster equipped with video compression tools, combined with software, will turn a PC into a non-linear editing system. We will call such devices video input/output cards (hereinafter referred to as input/output cards).

Compression

This parameter is one of the most important, determining the quality of video signal digitization by the board, so we will tell you about it in more detail. The entire video data stream is too large to be recorded directly (if using a single hard drive for recording), and compression is used to reduce it. Naturally, this reduces the quality of the video material, so the lower the compression, the better the quality, but the more disk space each frame takes up, so you need to find an acceptable compromise. To better understand this parameter, you need to know the following: One full-resolution PAL video frame contains 768x576=442368 pixels. Most modern boards use 4:2:2 YUV sampling encoding. In this case, the brightness of the signal (Y) corresponds to 8 bits and four bits are allocated to each of the color difference components (U and V), for a total of 16 bits (2 bytes) per point. This means that one frame takes up 442368x2=884736Bytes=0.84375MBytes. Since the PAL standard uses a frame rate of 25 frames/s, the total stream of uncompressed video data will be 0.84375x25=21.1 MB/s, and for the NTSC standard - 17.6 MB/s. You should pay attention to this difference, since manufacturing companies usually indicate the minimum compression for the NTSC standard, and since the flow is lower there, the degree of compression is lower.

If data on compression is not available, then it can be judged indirectly - by the maximum stream or by the amount of video that fits in 1 GB, for which you can use the formula Kcompr = 21.1 / P (where Kcompr is the compression ratio P is the stream for a given board, MB/s) or table No. 4:

Compression level	Video capacity per 1GB	Highest achievable quality*	Video data stream, MByte/s
1:1 (no compression)			original
	1min 38sec	1min 56sec	D1, Digital Betacam
	3min 14sec	3min 53sec
	4min 02sec	4min 51sec
	6min 28sec	7min 46sec
	8min 05sec	9min 42sec
	9min 54sec	11min 34sec
	12min 08sec	14min 34sec
	16min 10sec	19min 25sec

Table No. 4. Comparison of the degree of compression.

The data is of course approximate, but the parameters of most digitization boards should not differ from them by more than 5-10%. There are now several boards that can be used to record video in digital form without compression. All of them use built-in dual controllers and require a minimum of four AV (AudioVideo) SCSI (WIDE SCSI) hard drives to operate. At the current price of these drives, the scope of application of such boards is quite narrow. Due to the high cost of storing one minute of uncompressed video material (approximately $350), such cards can be used mainly for high-quality dumping computer graphics and editing of short video fragments (advertising videos, clips, screensavers, etc.)