COMPRESSION RULES
One minute of pure, uncompressed and digitized sound requires approximately 10MB on a computer’s hard drive, as a result of which, for the vast majority, music files are stored in compressed form to save space. How long does a minute of uncompressed video take? For example, to place a 60-second video with a rate of 30 frames per second, a resolution of 720×576 pixels, and a color depth of 16-bit, you will need approximately one and a half gigabytes of free disk space. And this without taking into account the audio track. After these numbers, it is probably not necessary to explain why digital video is stored on our computers exclusively in compressed form.
There are several dozen popular compression formats that use different compression algorithms, respectively giving different results.
DV (Digital Video) is one of the first compression algorithms for video transmissions, the development of which began in 1993 jointly by several companies that are the largest manufacturers of video equipment (Sony, JVC, Panasonic, Philips and Hitachi). The DV format provides a low data compression ratio (5: 1) and is characterized by a high bit rate, so the output video file is quite large. So one minute of DV video takes about 200MB (1 hour – 12GB) on digital storage media.
This format is most commonly used for compression when shooting video with consumer digital cameras and professional camcorders. At the same time, due to the small compression ratio, the footage is obtained in very high quality and the compression procedure itself, which occurs in real time, does not require powerful technical components.
It is true that it is still inconvenient to store video on a home computer, and even more so on optical discs in DV format, as it takes up too much space. So the specialists had to think of additional compression algorithms, with the help of which it would be possible to reduce the size of a digital film several times more.
MPEG (Moving Picture Experts Group) is a complete family of digital information compression standards, developed and standardized by the group of experts of the same name, formed by the ISO organization in 1988.
The first fruit of its creation was the original MPEG-1 video and audio compression standard, and in 1993, with the involvement of JVC and Philips, its Video CD (VCD) specification was developed, which is known to many users. As the name suggests, VCD is a format for storing compressed video with normal CD audio.
The use of MPEG-1 algorithms for encoding allows you to receive a video stream of up to 1.5 Mbit per second with a frame resolution of 352×288 pixels for PAL or 352×240 for NTSC, after which a normal CD can store 74 minutes of video with VHS quality sound (like a normal VCR) …
In 1995, the most popular MPEG-2 standard was released, which later became widespread in digital video DVDs, as well as in the transmission of cable and satellite television signals. The image quality here is much higher than its predecessor: at 25 frames per second, the resolution is 720×576 pixels for the PAL system and for the NTSC system: 720×480 at 30 frames / s. At the same time, the average maximum transmission width is 9.8 Mbps, which is almost 7 times that of Video CD. Another indisputable advantage of MPEG-2 is the ability to store a five-channel audio track (Dolby Digital 5.1 and DTS).
The maximum capacity of a DVD double layer disc (DVD-9) is 8.5 GB, which can store up to three hours of maximum quality video. If you are offered a DVD with multiple movies at once, know that you are most likely expecting a low-quality picture like a Video CD with very low resolution and bit rate.
Together with MPEG-2, around the same time, the development of a new MPEG-3 standard began, designed to encode audio and video transmissions on high definition television with a data transfer rate of 20 to 40 Mbps. But very It soon became clear that a slightly modified version of the MPEG-2 standard can be used for these tasks, after which all further developments of MPEG-3 were discontinued and this standard is not used today.
It should be noted that quite often the term “MPEG-3” is associated with the popular MP3 audio compression technology. But this is fundamentally wrong, as its correct name is MPEG-1 Audio Layer 3.
Finally, in 1998, a new family of video compression formats appeared: MPEG-4. It was developed with the aim of improving image quality at low bit rates.
