MPEG-1
MPEG-1 (ISO / IEC 11172) is a standard of the Moving Picture Experts Group (MPEG) for lossy video and audio data compression .
MPEG-1 was developed in the 1980s (introduced in 1991) and has the goal of compressing films to the limited data rate of an audio CD played at normal speed (up to 1.5 Mbit / s). The result, with its rather poor quality, is called a video CD . The video compression of MPEG-1 was significantly refined and improved in 1994 by MPEG-2 .
Video coding method
The image format of MPEG-1 is similar to the JPEG format . However, the parameters are precisely defined:
- Image size maximum 768 × 576 pixels
- Ratio of the height to width of the pixels (14 aspect ratios defined)
- Frame rate in Hertz
- Images are in YCbCr format as 3 × 8-bit values per pixel:
- Y: luminance / brightness component (16: black, 223: white)
- C r : red-green color difference component (−112: green, +112 red)
- C b : blue-yellow color difference component (−112: yellow, +112 blue)
| Image type | purpose | compression |
|---|---|---|
| Intra picture (English intra coded picture, I-frame ) | An I picture corresponds to a still picture. It serves as an anchor for random access. | low (similar to JPEG, but in real time ) |
| P-picture (English predictive coded picture, P-frame ) | P-pictures require information from previous I-pictures or P-pictures. | greater compression than I-pictures |
| B-picture (English bidirectional coded picture, B-frame ) | B-pictures are dependent on the preceding and following I-pictures or P-pictures. | greatest compression |
| D-picture (English DC direct coded picture, D-frame ) | D-pictures are used for fast forwarding. | only one color value is stored per 8 × 8 block |
In image processing, the images are compressed to different degrees and used for different purposes. The I-pictures are compressed independently of other pictures - they require the most storage space, but can be decoded independently of previous pictures. Therefore they are necessary to be able to jump (almost) arbitrarily in a video. Other images are encoded as a function of the other images in the video stream and therefore require less storage space. These types of images are then dependent on the encoder, its settings and occasionally different frequencies used by the images and typically occur cyclically as so-called group of pictures (English Group of Pictures, GOP ) on. A group extends from one I-picture to the next. The groups are often half a second long.
Audio coding method
The standard also includes three audio coding methods. In increasing complexity and quality, these are layers 1, 2 and 3.
The Audio Layer 1 - also known as MP1 - was developed by Philips as a low-Complexity version of the Audio Layer 2 incorporated into the standard. The digital compact cassette from Philips, which came onto the market at the same time as Sony's MiniDisc and is no longer manufactured, used this process with a data rate of 384 kbps.
The Audio Layer 2 - also known as MP2 or Musicam - was the established standard in radio beings. Almost all professional digital playback devices used MPEG-1 audio layer 2 with a compression of 256 kbit / s (128 kbit per second and channel), as it could then be easily transmitted via the ISDN infrastructure that is widely used in Europe . Audio Layer 2 is also used on Video CDs and Super Video CDs as well as (rarely and only approved for Europe) on DVDs and digital television .
The Audio Layer 3 - better known as MP3 - was developed by the Fraunhofer-Gesellschaft develops and others and was, like Layer 1 and Layer 2 is not a license. This means that manufacturers who wanted to develop and sell an encoder for MP3 had to pay license fees for it. Encoders not sold commercially (such as LAME ) are license-free.
The comparatively good ratio of size on the one hand and quality on the other led to the triumph of the MP3 format in the 1990s. It was the basis for the flourishing of online file sharing sites (such as Napster ) and mobile music players ( MP3 players ) based on flash memories or hard drives . MP3 was further developed to the following advanced audio coding standards (from MPEG-2 and MPEG-4).
System definition
Finally, MPEG-1 defines a method for interlacing (“multiplexing”) audio and video into system streams in blocks . This also includes data on playback times and error detection, among other things. They can be saved as a file or streamed over a network . MPEG-1 System Streams was designed for media insensitive to interference (VCD) and is identical to the program stream defined in MPEG-2 .
See also
literature
- Roland Enders: The home recording manual. The way to optimal recordings. 3rd revised edition, revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .
- Thomas Görne: Sound engineering. Fachbuchverlag Leipzig by Carl Hanser Verlag, Munich a. a. 2006, ISBN 3-446-40198-9 .
- Hubert Henle: The recording studio manual. Practical introduction to professional recording technology. 5th completely revised edition. Carstensen, Munich 2001, ISBN 3-910098-19-3 .