Digital video: an overview of formats
Recently, home users have the opportunity to create digital videos with their own hands. It goes without saying how convenient it is to store family video files in this way. Digitized records do not deteriorate over time, do not lose quality when copied, and can be easily edited. Video compression technologies, which continue to improve even now, played an important role in its distribution.
First, let’s find out why compress video. To understand this, let’s move on to the basic principles of digitizing moving images.
The video sequence is formed from consecutive 720 x 576 pixel frames, which are changed 25 times per second (according to the PAL standard). If you scan them with 16-bit color depth, each frame will take up about 1.2MB, which means that to store 1 second of video, you’ll need about 30MB of disk space, and about 150GB will go to one movie. 1.5 hours. This is at least five times the capacity of hard drives found in modern home computers. Try to figure out how many 650MB CDs you need to burn one of these movies. To reduce the size of files containing digitized video, various data compression algorithms are used. There are two types of algorithms that work, respectively, without loss of information and provided.
Lossless compression (with virtually no degradation of image quality) in digital video is done using methods similar to those used in archivers such as WinZIP or WinRAR. However, due to some peculiarities of the video information, such algorithms in this case are not efficient enough (the minimum size of a compressed file is 1/3 of the original) and therefore it is practically not used.
Lossy compression is the main method of reducing the size of video files. These algorithms allow us to determine that part of the information that the viewer, most likely, will not notice when watching a movie, and remove it from the file. The main digital video formats using lossy compression today are Apple QuickTime, Intel Indeo, MPEG-1, MPEG-2, MJPEG, and MPEG-4. The specifications of the MPEG-7 standard are also under development, but it is still too early to talk about it.
Apple QuickTime
The MOV file format was developed by Apple for Macintosh computers and later ported to the PC platform. From 1993 to 1995, this format was dominant. Its latest version, number 4.1, allows you to transfer data in streaming mode. This means that you don’t need to fully download the file to start watching the video. However, with the advent of MPEG specifications, this format is gradually losing popularity. Its main problem is that the QuickTime standard is closed. Apple keeps secret the methods by which video is encoded. Consequently, third-party programmers cannot write programs that compress video in this format.
Intel Indeo
This format was developed by Intel Corporation to compress video data using the new capabilities of the Intel Pentium MMX processor. In addition to supporting streaming and copyright protection features, this standard implements several features that were innovative at the time of its introduction. It allows you to apply various effects to a video sequence (for example, change the brightness or contrast) in real time, decode not the whole frame, but, for example, the central fragment, make part of the frame of a video transparent and superimpose two videos one on top of the other. The latter effect is often used in television news programs, when a commentator is depicted in front of a video report of the scene.
However, the Indeo format is not widely used. And with the release of MPEG-4, which also contains all these features, this standard generally doesn’t work.
MPEG-1
The MPEG-1 video compression format was developed by the Motion Picture Expert Group, an international organization that creates video compression standards. It supports a maximum frame resolution of 4095 x 4095 pixels at a frame rate of up to 60 times per second.
