What are Codecs?


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What are Codecs

CODECS

Whether you make your own video and audio files available on the Internet or want to use existing resources, there are a host of different player programs, codecs, and file formats available. Here we guide you through the jungle of MPEG, AVI, MKV & Co. On the one hand, the relationships between the different components of the system are explained. This will solve puzzles for example why only certain AVI videos are displayed on your computer and how you can solve such problems. On the other hand, the advantages and disadvantages of the different formats and methods are explained. In this way, you can evaluate what quality you can expect from an audio or video file and which files are particularly suitable for your purposes.

Codecs

As an end user, you are particularly familiar with one type of program: playback programs (or “players”). They play audio or video files and are therefore the software equivalent to CD or DVD playback devices. The program interface contains elements of a remote control: there are buttons for play, forward, backward, pause, etc. B. Windows Media Player, VLC Player, or Apple iTunes. Instead of inserting a data carrier, the files must be opened on the software players. Audio and video files can only be opened by a player if it can do something with the file format used.

File formats

The digital data with which analog video or audio signals are represented can be organized in various formats. This can best be explained for a single image – there are multiple ways to store individual pixels in a file. For example, if the image points are stored one after the other from left to right or first from top to bottom in the file it is of course a convention that must be specified. The way a color value is stored must also be clearly defined. These and many other specifications are determined by the respective file format. To store the data, a predefined encoding rule is always followed, which is ultimately decisive for the data to be interpreted correctly. Perhaps the difference between individual formats is better understood if you think of them as different data carriers: CDs, large and small discs, tapes, etc. they may contain audio data, but you still cannot put a disc in the CD player! The MPEG, Quicktime or Matroska formats are equally different. These formats are also known as container formats. The container can easily be imagined as a box that in turn contains various audio and video codecs. These codecs can encode and decode files, that is, compress a signal for transport, and then decompress it again during playback. if you think of them as different data carriers: CDs, large and small discs, tapes, etc. can contain audio data; however, you cannot put a disc in the CD player. The MPEG, Quicktime or Matroska formats are equally different. These formats are also known as container formats. The container can easily be imagined as a box that in turn contains various audio and video codecs. These codecs can encode and decode files, that is, compress a signal for transport, and then decompress it again during playback. if you think of them as different data carriers: CDs, large and small discs, tapes, etc. can contain audio data; however, you cannot put a disc in the CD player. The MPEG, Quicktime or Matroska formats are equally different. These formats are also known as container formats. The container can easily be imagined as a box that in turn contains various audio and video codecs. These codecs can encode and decode files, that is, compress a signal to transport it and then decompress it again during playback. The MPEG, Quicktime or Matroska formats are equally different. These formats are also known as container formats. The container can easily be imagined as a box that in turn contains various audio and video codecs. These codecs can encode and decode files, that is, compress a signal to transport it and then decompress it again during playback. The MPEG, Quicktime or Matroska formats are equally different. These formats are also known as container formats. The container can easily be imagined as a box that in turn contains various audio and video codecs. These codecs can encode and decode files, that is, compress a signal to transport it and then decompress it again during playback.

Many different codecs for playing video and audio data
In the living room, the various playback devices are often combined into one system, so multiple devices are not necessary. Different playback programs work the same way: they can read and play different formats. A separate codec is used for each format. These are snippets that only do one job: encode and decode audio or video information. Each codec can be used to write and read exactly one format. Different codecs are used for different formats; correspond roughly to the individual technical components of your stereo system. But instead of a K device for playing discs and a C device for playing DVDs, there is an M codec for playing audio in MP3 files and a W codec for playing video according to the MPEG-4 standard in MP4 files. Most of the players already have multiple codecs built in and therefore can play multiple file formats. There is also the possibility for a player to learn to understand other file formats by adapting additional codecs. Just as you can connect additional devices to your stereo system, such as an old record player or a high-end CD player, the players can be upgraded with plug-ins. A codec plugin is independent of a specific player and can be used by different players. Additional codecs are required, eg. Eg B. if you want to play newer or rarely used file formats with your playback software.


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What does a codec indicate?

The six most important specifications to know about a codec are: codec type, resolution, compression, GOP, bits and color sampling.

Type of codec:

here come the little names of maras. H.264, MPEG-4, MPEG-2, H.265 … will give us an estimated indication of the efficiency of the codec, although as I indicated above, be careful because it can be misleading. Nothing like comparing the material directly. Within each one, the rest of the specifications are defined below, there being generally different variants in each.

Resolution:

number of vertical and horizontal lines. Mind you, it is another one of those deceptive factors, the real resolution that a camera gives has little to do with the resolution of the codec, nor does any of this have to do with the sharpness. We will expand this in another chapter.

Compression:

In Mbps or Mbit / s, it indicates the information contained per second

GOP:

Group of Pictures, specifies the order in which images are stored. It can be Intra, where each image is independent, or employ various methods where an independent reference image is used and others are stored next to it containing information regarding movement compensation. That is, it stores an image, and the differences in a certain group of the following, until you have a complete image again. Example: GOP12, if we record at 24fps, it will contain two complete images at half-second intervals, and 11 will start from it, only saving the differences from the whole image.

Bit Depth:

the more bits, the more information we will have available, allowing us a more aggressive grading and thus avoiding banding.

Color sampling:

Broadly speaking, it indicates the way in which the chrominance is compressed. We will make a chapter dedicated to this, since it is a complex and important factor.

Codec Standards

Each codec has a series of variants within it, and sometimes these variants are used without specific names or certain new variants. There are some codecs however whose specifications are already fully predefined. For example, there are the well-known Apple Prores, used in assembly regardless of the codec with which we record (some professional cameras and external recorders have it incorporated), or the most used in AVCHD and XAVC S consumer cameras.

However, we must bear in mind that even with a predefined specification there can be huge differences from camera to camera. And there are many other factors to consider, since the internal processing of the video will be crucial for the subsequent compression process.

The (little) importance of bitrate

Bitrate defines the data that will be saved per unit of time, usually expressed in Mbps (megabits per second, not to be confused with megabytes). It may seem a priori that a greater amount of data per second means higher quality, but here comes the codec efficiency factor, and the truth is that we must compare the material directly (and without extra compression from YouTube or Vimeo) to Really see the differences.

An example can be seen in the Panasonic GH4. This camera has many bitrates to which we can record and also several resolutions. Something curious, is that if we record at Full HD, we can use a bitrate of 200 Mbps, while if we record in 4k, the bitrate is 100 Mbps. This can lead us to think that if the material is going to be broadcast in Full HD, it will be better to use this resolution and the higher bitrate. However, the reality is that it is better to rescale the 4K and use its lower bitrate: we will get better quality. It can be easily observed even with the compression of Vimeo in the video by Andrew Reid.

Another example is the Canon C100, a camera with very striking specifications and really good results. It uses the AVCHD codec (MPEG-4 AVC 25Mbps 4: 2: 0), which has never had a good reputation. Its quality is such that the differences with its older sister the C300 (MPEG-4 50Mbps and 4: 2: 2 color sampling) are negligible. Even using an external recorder like the Ninja Atomos, the differences are almost nil, even if it uses Prores and the output is 4: 2: 2. What’s more, broadcasting in Full HD its sharpness is superior to a GH4 with 4K rescaling. It is the magic of video.