Video Codecs 101

I have been working a lot with video lately at work and to work with digital video it often helps to know a little bit about the technology, I thought I would share with you all, some basic concepts behind digital video in particular this term called codec. Essentially, a codec is a mathematical formula that reduces the file size of a video or audio file. When a codec reduces a file size of a video file, it is also said to be compressing the file. There are two forms of compression – Lossless and Lossy Compression. Lossless compression – is the process of compressing data information into a smaller size without removing data. To visualise this process imagine a paper bag with an object in it. When you remove the air in the bag by creating a vacuum the object in the bag is not affected even though the total size of the bag is reduced. Lossy compression – is the process of ‘throwing away’ data to reduce the file size. The compression algorithms used are complex and try to preserve the qualitative perceptual experience as much as possible while discarding as much data as necessary. Lossy compression is a very fine art. The algorithms that enable this take into account how the brain perceives sounds and images and then discards information from the audio or video file while maintaining an aural and visual experience resembling the original source material. But, I know, everyone wants to know about the quality right? Well, the quality of digital video is determined by the amount of information encoded (bitrate) and the type of video compression (codec) used. While there are some codecs that can be considered to be more advanced than others, the difference in perceived quality is not significant. Yes, codecs reduce the necessary bitrate of a media file by describing the media in clever, more efficient ways. Video codecs basically describe the changes between one frame and the next, instead of describing each frame separately. So, remember, codecs use complicated mathematical techniques to encode video, you will need a powerful chip to decode that video quickly enough for playback, this is a reason why sometimes it’s best to use a simpler codec. Anyways, hope this is a small insight to video codecs and what they do.