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Multimedia Codec: How to compress videos, images, and audio!

A codec is an essential element for the multimedia era. Indeed, every day we work with files such as images, audio, and videos. All of them need these elements to work properly. But do you really know what it is and how it works. If not, here we explain it in detail.

What is a codec?

A codec is a hardware or software-based process that compresses and decompresses large amounts of data. The function of codecs is for applications to play and create multimedia files for users. Other functions are to send multimedia files by streaming. The term is a combination of the words coder and decoder.

Codecs compress, or shrink, multimedia files such as videos, audios and still images. In this way, they aim to save space on devices and efficiently send those files over a network faster.

Codecs are invisible to the user. In fact, they are present in the software or hardware of a device. That is, there is software that acts as a codec. To do so, they use the CPU for encoding and decoding. There are also accelerators running in hardware. That is, they use a specific processing unit to accelerate encoding and decoding. The latter is the case of AV-1 engines implemented in current graphics cards.

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The main function of a codec is data transformation and encapsulation. We can have audio, image or video codecs. Video codecs usually include both image and sound codecs at the same time. In fact, video is nothing more than a series of frames passing through.

Codecs use an algorithm to convert data into a sequence of bytes different from the original. In this way, they achieve their purpose, which is to reduce the file size or space occupied.

The higher the bit rate, the lower the compression. And lower compression generally means higher quality, or closer to the original, in general. Some codecs create smaller files with reasonably acceptable quality. Other codecs create efficient files that have higher quality but take up more space. Other codecs create small, efficient files, but lack overall quality.

What is coding?

Encoding is a process used to compress multimedia data, such as videos, audios, and images. This in order to reduce the size of the files. In addition to facilitating their transmission and storage. This is done at the moment of recording or creating the media file in question, or after editing it. Encoding is possible in two ways:

  • Lossy compression: Is a method of data compression in which some redundant or less important information is removed to reduce the file size. By removing data, there is a loss of quality in the original content. It is widely used in multimedia data compression. For example, such as audio and video. In fact, there, the loss of certain details is not relevant to the human ear or eye.
  • Lossless compression: Data compression: is a method of data compression that reduces the file size without losing information or quality of the original content. In this case, we could recover all the information deleted in the compression process. It is enough to decompress the file. Consequently, data loss is a real possibility.

Steps to perform coding

  • Content analysis: First, the codec analyzes the multimedia content. Whether it is audio, video, or images. In this way, it seeks to identify relevant patterns and characteristics. This helps the codec determine which parts of the content can be compressed most effectively.
  • Transformation: In this phase, the multimedia data is mutated to a more efficient mathematical representation. For example, in the case of video, there are transformation techniques such as the discrete cosine transform (DCT). In this way, they will represent the pixels in a more compact way.
  • Quantization: In this step, the numerical values resulting from the transformation are quantized or rounded to discrete values. Quantization is a key technique for lossy compression. Indeed, it allows eliminating less important details and to reduce the precision of certain values.
  • Compression: This is where data compression is actually achieved. The codec uses different techniques. For example, delta coding, Huffman coding or arithmetic coding. In doing so, it aims to represent the quantized data more efficiently. During this process, redundant or irrelevant data is removed or represented in a more compact form.
  • Packaging: once the media data has been compressed, it is packaged in a container format. The container will include the compressed information along with metadata. In addition to other related information, such as audio tracks or subtitles.

What is decoding?

Decoding is the reverse process of encoding. That is, the procedure by which a set of encoded or compressed data is restored to its original form. In doing so, we restore the information and structure prior to encoding.

When applying some type of encoding or compression to data, the objective is to reduce its size. This makes it easier to store, transmit or process. However, to use this data again, it is necessary to perform the decoding process to recover the original information.

Steps for decoding

The decoding process is the opposite of the encoding process. Therefore, the steps would be:

  • Receiving and opening the file: begins when the compressed and packaged media file arrives. The media player or the appropriate application opens the file to start the decoding process.
  • Data extraction: the application extracts the compressed information from the archive. This information includes the compressed media data along with metadata. In addition to other relevant information stored in the container.
  • Decompression: the application uses the appropriate codec to decompress them.The file may be lossy. Consequently, decompression will involve restoring the data to its original form. However, we may lose quality compared to the original uncompressed file.
  • Inversion of quantization: if the encoding process included quantization, decoding must perform the reverse process. That is, restore the quantized values to their original values.
  • Inverse transformation: It is likely to have used some mathematical transformation in the coding process. Then, the decoding must perform the inverse transformation to return to the original representation of the data.
  • Data reconstruction : After decompressing and transforming the data to its original form, the application can reconstruct the multimedia data. For example, in the case of video, we can restore the frames and image sequence to play the original video.
  • Playback or display: Finally, the multimedia data is output to the output device, such as a display or speaker. In this way, the user can watch or listen to the multimedia content in its original form.

What is transcoding?

Transcoding is the process of converting a media file from one encoding format to another encoding format. In this process, we extract the information present in the original file and recode it into a new format. This involves a conversion of the data to suit the characteristics and requirements of the target format.

Transcoding is only available between some types of codecs or formats. Indeed, it is not possible, for example, to transcode or convert a text to use an audio codec. It is possible to convert from audio to audio, from video to video, from image to image, etc.

Difference between container format and codec

It is important to know the differences between codec and container. Indeed, it is something that many users often confuse:

  • Codec: is an algorithm or set of algorithms whose function is to compress and decompress multimedia data. For example, audio, video, or images. Codecs are responsible for encoding the original information into a more compact format for storage or transmission. In addition, they then decode it again for playback or display. There are both lossy and lossless codecs. Therefore, it means that some compress the data by removing some information (lossy). On the other hand, others compress without losing information (lossless). Examples of common codecs are H.264, AAC, MP3, VP9, among others.
  • Container: Also known as a file format. It is a structure that stores multimedia data compressed with a codec along with additional information. For example, metadata, subtitles, and audio or video tracks. With containers, we can group all these elements in a single file. This facilitates the handling, storage and transmission of multimedia files. Containers do not directly affect the quality of the content. In fact, they simply organize and store the compressed data with codecs. Examples of popular containers are MP4, MKV, AVI, MOV and FLAC.
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