MPEG-1 How it works Part 2
Mpeg-1 video
In this case, part of the information is lost due to the alignment of strongly differentiated areas that do not obey the correlation. After this procedure, the quantization algorithm comes into play: quantization, which forms the quantization matrix. The quantization matrix is a quantization matrix whose elements are continuous to discrete data, that is, numbers representing the amplitude values of the Fourier frequency components. After the formation of the quantization matrix, the frequency coefficients are divided into a specific number of values. The precision of the frequency coefficients is fixed at 8 bits. After quantization, many of the coefficients in the matrix are set to zero. And as a final stage, the matrix is transformed into a linear shape. whose elements are data continuously converted to discrete, that is, numbers representing the amplitude values of the Fourier frequency components. After the formation of the quantization matrix, the frequency coefficients are divided into a specific number of values. The precision of the frequency coefficients is fixed at 8 bits. After quantization, many of the coefficients in the matrix are set to zero. And as a final stage, the matrix is transformed into a linear shape. whose elements are data continuously converted to discrete, that is, numbers representing the amplitude values of the Fourier frequency components. After the formation of the quantization matrix, the frequency coefficients are divided into a specific number of values. The precision of the frequency coefficients is fixed at 8 bits. After quantization, many of the coefficients in the matrix are set to zero. And as a final stage, the matrix is transformed into a linear shape. After the formation of the quantization matrix, the frequency coefficients are divided into a specific number of values. The precision of the frequency coefficients is fixed at 8 bits. After quantization, many of the coefficients in the matrix are set to zero. And as a final stage, the matrix is transformed into a linear shape. After the formation of the quantization matrix, the frequency coefficients are divided into a specific number of values. The precision of the frequency coefficients is fixed at 8 bits. After quantization, many of the coefficients in the matrix are set to zero. And as a final stage, the matrix is transformed into a linear shape.
All these transformations concern only the image. But in addition to the image in almost any video clip, there is also sound. Sound encoding is done by a separate audio encoder. As the MPEG format has evolved, audio encoders have been modified several times to be more efficient. At the time of the final standardization of the MPEG-1 format, three audio encoders of this family were created: MPEG-1 Layer I, Layer II and Layer 3 (the same famous MP3). The coding principles of all these codecs are based on the psychoacoustic model, which was further refined and reached its apotheosis for the MPEG-1 family in Layer-3 algorithms.
Many articles have been written on the psychoacoustic model and the principles of lossy audio data compression, in particular the article “Description of MP3 audio compression format”, which you can read on this site, so it can be skipped the description of the audio encoders, mentioning only the synchronization of audio and video data and audio track formats.
The synchronization of audio and video data is carried out using a specially dedicated data stream called a system stream. This sequence contains a built-in timer that operates at a speed of 90 KHz and contains 2 layers: a system layer with a timer and service information to synchronize frames with an audio track and a compression layer with audio and video sequences.
The service information refers to various kinds of marks, the most important of which are the marks SCR (System Clock Reference), the codec time counter increment and PDS (Presentation Data Stamp), the beginning mark of the video frame. or audio frame playback.
Well, the story about MPEG-1 has almost come to an end, it only remains to name a few parameters of the audio tracks that are used in this format.
The quality of audio tracks in MPEG-1 can vary widely, from high quality to ugly. Finally, all audio compression formats were standardized in 1992 by the European Commission for ISO standards.
