Multimedia

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1.       Sound

Computers until the end of the 1980s were not built to import and reproduce sound, since there was no suitable hardware and software for this purpose. Often there was a small built-in loudspeaker, which was suitable for low-quality sound. Computer sound processing systems were very specialized and expensive. Since the 1990s, cards began to spread extension for good quality audio input and playback, at affordable prices. With these possibilities and the great development of the Internet, which had begun at that time, new possibilities began to be offered to computer users. Today, we cannot conceive of a computer, small or large, that does not provide the user with a rich and high-quality multimedia experience

2.       Digital audio and sound digitization process

In digitization, the sound from the microphone is converted into an electrical signal, which is channelled into an integrated circuit, the analogue to Digital Converter (ADC). This converter takes samples (measurements) of the sound at a certain rate, which is called the sampling rate, and we measure it in Hz. Each sample (measurement) is then converted into a corresponding digital number, which is represented as a series of bits (usually 8 or 16 bits).

3.       Video

Computers today are largely used for video playback. Usually, in the video sense one perceives the cinematographic or other films that a person can see on the computer. In the category of video, however, cartoons and many games can be included, because their depiction has the same characteristics as those of films. Also, we should not forget that the computer can be used both for creation and for video editing.

4.       What are the features of a digital video?

A video actually consists of several images of the same size, placed one after the other, which are presented at a fast enough pace, so that the eye (and the brain) creates the illusion of movement.

The main features of a video are the following:

•         Frame size in pixels (in the language of video production each picture is called frame), for example 640×480.

•         Colour depth (colour depth), i.e., how many bits each is composed of Pixel (for example: 4, 8, 24) of each frame. It is exactly corresponding to the colour depth we have already encountered for the pictures.

•         Frame rate, i.e., how many frames (images) are displayed sequentially each second. Measured in frames per second (fps), for example, 50 fps. It is corresponding to the sampling rate of sound.

Interlacing is a method used to double the frame rate, without doubling the information when sending the video. Because the eye is more sensitive to low frame rates (where the image seems to flicker) than to the detail of the image, only the odd rows of pixels of one frame and the even ones of the next are sent, so that when presented interchangeably the rate of rotation is faster and the image smoother.


EXERCISES:

1. Work in groups to apply everything you learned to create a small movie using sound and videos.