Confusion between codec and container is very common. And even more if we add file extensions, such as .flv, .mp3, .mp4, etc.
What is a codec?
The codec term comes from the concatenation of the initials of two words: encoder and decoder. Strictly speaking, a codec is a specification on how to code a type of information and then be able to decode it. For example, a codec determines how video and audio information is compressed and decompressed. Remember that compression is a specific case of coding in which space is reduced, eliminating redundant or low perceptual impact information.
Coding means something like compressing. That is, it seeks to reduce the amount of bits that an audio file occupies. The idea is to reduce the amount of bits while maintaining the highest possible audio quality.
Obviously, once the files have been compressed, they need the counterpart, which becomes the decoder that is the one that can interpret and reconvert in sound what was written in the file.
Then, a codec is one that serves to compress and decompress (encode and decode) an audio or video file.
What is a container?
Within the multimedia scope, a container is a specification on how different types of encoded multimedia content are sorted within a file. These different contents are usually, mainly, video, audio and text.
Consider the case of a movie in digital format. This movie is in a file. When we open that file, a player runs and we can enjoy the movie. Notice that a movie has video, has audio, subtitles, information about its author, information about its duration, etc. For the convenience of the user, all these elements are grouped into a single file. The order in which they are saved in that file is the container specification.
Connection
The video information that is inside a container is usually compressed, that is, it usually follows the specification of a specific codec. The same goes for audio information. The confusion appears when there are containers and codecs with very similar or even equal names.
The most popular
The most popular video codecs currently are Theora, VP8, MPEG-2, h.264, Xvid and Divx. Regarding audio codecs: AAC, FLAC, MP3, Vorbis (ogg) and WMA are the most abundant.
The most commonly used containers are AVI, Divx, Matroska, Flash video, MP4, MPEG, Ogg, Quicktime, MXF and WebM. Since the containers are intrinsically linked to the files, each of them also specifies one or several possible file extensions:
AVI -> .avi
Divx -> .divx
Matroska -> .mkv, .mk3d, .mka, .mks
Flash video -> .flv, .f4v
MP4 -> .mp4
MPEG -> .mpg, .mpeg
Ogg -> .ogg
Quicktime -> .mov, .qt
MXF -> .mxf
WebM -> .webm
And to open a container and see its contents?
The containers are interpreted through a media player application, such as Windows Media Player, Quicktime (application with the same name as a container), VLC, Plex, RealPlayer or Winamp, to name a few .
A good option is the VLC player, as it offers compatibility with all formats under almost any platform and even allows you to play incomplete files (useful feature if you want to start playing an audiovisual content that has not yet finished downloading, provided that this be progressive). In addition, it is freely distributed.
