Easily interpret Audio/Video Encoding

Author: Hu Zhenyu

Recently, many of my friends have asked me some questions about audio/video encoding and decoding. This is probably because of the popularity of mobile phones, PDAs, and other devices and the increase in bandwidth, the spread of audio and video is becoming more and more popular.

However, I found that many of my friends are still unclear about some basic concepts, especially encoding and file formats. Here I will give a brief introduction to the basic audio and video knowledge.

Audio/Video Encoding and file formats (containers) are a very large field of knowledge. To make it clear, you need to write a textbook. Here are a few simple concepts:

First, we need to identify the differences between media files and encoding:

A file is a collection of videos, audios, and even scripts. It can also be called a container;

The compression algorithm of the video and audio in the file is the specific encoding.

That is to say,. in an AVI file, the video may be encoded as A or B, and the audio may be encoded as 5 or 6. The specific encoding decoder is used, the player reads the information in the AVI file format and calls it.

Encoding introduction:

There are many audio and video encoding solutions, which cannot be described as excessive. Currently, the following types of common audio and video encoding are available:

MPEG series: (developed by the mpeg [Motion Image Expert Group] affiliated to ISO [International Standards Organization)

Video Encoding mainly involves mpeg1 (which is used for VCD), MPEG2 (used for DVD), and MPEG4 (currently DVDRip uses its variants, such as DivX and Xvid) MPEG4 AVC (currently popular );

Audio Encoding is mainly MPEG audio layer 1/2, MPEG audio Layer 3 (famous MP3), MPEG-2 AAC, MPEG-4 AAC and so on. Note: No MPEG is used for DVD audio.

H.26x series: (led by ITU [International Telex video Alliance], focusing on network transmission. Note: Video Encoding only)

Including h261, h262, h263, h263 +, h263 ++, and h264 (the crystallization of MPEG4 AVC-Cooperation)

Microsoft Windows Media Series: (Can you set your own standards ...)

Video Coding Mpeg-4 V1/v2/V3 (based on MPEG4, divx3 source, huh, huh), Windows Media video 7/8/9/10

Audio Encoding: Windows Media audeo V1/v2/7/8/9

Real Media Series: (Note that the real encoding here is not an RM or rmvb file)

Video Encoding: realvideo G2 (early stage) and realvideo 8/9/10

Audio codes include RealAudio cook/sipro (earlier) and RealAudio AAc/aacplus.

QuickTime series: (a platform with many encoders)

Video Encoding includes Sorenson video 3 (for qt5, standard), Apple MPEG-4, Apple H.264

Audio Coding qdesign music 2, Apple MPEG-4 aac (this is good)

Others, such as: Ogg, On2-vpx, flash vidio: not detailed.

It is particularly noted that the audio encoding of the media such as DVD adopts several relatively independent types, which are listed as two common ones: AC3 (developed by Dolby) and DTs.

File Format (container ):

Avi

Audio/Video interaction storage, the most common audio/video container. The most supported video and audio encoding is supported.

MPG

The audio and video containers used by MPEG encoding have the characteristics of stream. PS is classified into ps, ts, etc. PS is mainly used for DVD storage, and Ts is mainly used for HDTV.

Vob

DVD adopts the audio and video container format (I .e. video MPEG-2, AC3 or DTS for audio), supports multi-video, multi-track, multi-subtitle chapter, etc.

MP4

MPEG-4 coding uses the audio and video container, developed based on QuickTime mov, has many advanced features.

3GP

The 3GPP video format is mainly used for streaming media transmission.

ASF

The audio and video containers used by Windows Media can be used for stream transmission and include scripts.

Rm

The audio and video container used by RealMedia for stream transmission.

Note: rmvb is the file format (container) in which the video encoding part adopts Variable Bit Rate compression)

MoV

The QuickTime audio and video container is probably the most powerful container today, and even supports VR technology, Java, and so on. Its variants MP4 and 3GP are not so powerful.

MKV

MKV can combine Windows Media video, realvideo, MPEG-4 and other video audio into a file, and supports multi-track, Chapter subtitles and so on.

Wav

A type of audio container (Note: It is only audio). Generally speaking, WAV is a PCM code without compression. In fact, WAV can also include other ACM compression codes such as MP3.

MP3

As mentioned above, do you have to say more? It is MPEG audio Layer 3 (an audio encoding of MPEG 1)

The knowledge about audio and video is too complex. Here we will give a brief introduction to some basic and beginner knowledge, for example, for each encoding algorithm and file format specification, You need to refer to relevant professional books and materials. Of course, you can continue to pay attention to my series of articles.