A video codec is a software that compresses or decompresses digital video files. A video codec converts an uncompressed format to a compressed format and vice versa.

In most cases, the compressed data format follows a specific compression specification. This specification is usually lossy in the case of video files, which means that not all the information contained in the original video file is retained.

In the first video codecs only single still images were compressed, newer methods use similarities of successive partial images for compression.

Compression methods are based on either redundancy reduction or irrelevance reduction. In the first case, static properties of an image signal are used to save as much memory space as possible. This type of compression is lossless.

The irrelevant reduction procedure omits information below the typical human visual threshold. This can be achieved, for example, by reducing color information or varying the frame rate. However, these methods are usually lossy, but offer a much higher compression factor.

The most common codecs and their advantages/disadvantages are:

H.264/MPEG-4

H.264 also AVC (Advanced Video Coding) is the most widely used codec. Supports resolutions up to 8K. Compared to the previous codecs H.263, MPEG-2 or MPEG-4 Part 2, H.262 offers much higher image quality and/or higher image compression. H.264 is also suitable for a wide range of applications because it offers high flexibility in bit rates and resolutions.

H.265/MPEG-H

Also known as HEVC (High Efficiency Video Coding), the successor to H.264, this codec offers twice the compression rate at the same image quality or substantially improved quality at the same data rate compared to H.264. Resolutions up to 8K are supported.

VP8/VP9

VP8 and VP9 were developed by Google and are mainly used for the YouTube video platform. Both are open formats and compete mainly with H.264 and H.265. This family of codecs offers a relatively high compression factor with high image quality.

Apple ProRes

A proprietary codec developed by Apple that is mainly used in post-production. Therefore, this codec is not recommended as an end user format. Apple ProRes is a lossy compression and offers a color depth of up to 12bit and a maximum resolution of 8K.