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Digital Video Basics – Codecs Explained

Digital media has permeated everyday life for most of us – pictures, music, video are largely transported, viewed, stored and shared in a digital format. Older forms of media still exist of course. For instance, vinyl records are experiencing a renaissance. However, the dominance of digital is primarily because internet, computer and smartphone usage continues to grow exponentially and the need to view, watch and listen anywhere at any time means things like dvd, cd and paper photographs are no longer convenient for many users. While turning content into 1’s and 0’s isn’t a new concept, digital entertainment requires software called codecs in order to listen or watch. So what exactly is a codec?

Simply put, codecs are compression technologies; compression of music and video is necessary for the purpose of transportation since raw audio and video files are far too large to upload, download or transport on their own. Compressing these files down into a smaller version of themselves allows for far more efficient storage and delivery. A codec is vital to this process as it is the software that makes compression and decompression possible. Codecs have two primary components – an encoder, which compresses or shrinks the file, and a decoder that decompresses the file and makes it listenable or viewable. There are many different types of codecs for various uses – data (PKZIP), still images (PNG, GIF, or JPEG), audio (MP3, AAC, FLAC) and video (MPEG-2, DivX, XviD, H.264) – and they generally are categorized in two ways, they are either considered ‘lossy’, or ‘lossless’.

The difference between lossy or lossless is as such – a lossy codec means a reasonable facsimile of the original content is produced upon decompression; the codec essentially removes small bits and pieces of information during compression that will not generally be noticeable to the ear or eye when the content is used. A lossless codec means that compression does not remove any parts of the information and decompression produces an exact replica – full sized – of the original content. Lossy codec use enables more files to be stored or sent or received, but the tradeoff is not palatable for some users as lossy codecs will only ever produce a slightly inferior version of the original material. An example of lossy codec use is when you watch streaming video; generally, the data rate must be kept low enough to allow for uninterrupted streaming, which means you aren’t seeing the image in its original resolution quality.

Lossless codecs tend to be used more often when it comes to audio files (example: FLAC is a lossless codec used by many audiophiles) while with video, lossless codecs use high data rates that don’t always play nice when it comes to streaming or viewing on certain devices or operating systems. Many codecs are function specific in nature; for example, many camcorders use codecs that have been developed to capture at a high data rate while still meeting data rate requirements of the camcorders on-board storage. In addition, the captured data must also be able to be played back on a computer or television without any inconvenience to the user. It is for reasons such as this that codecs are always evolving to encompass more and more formats as well as expanded playback capability; in a perfect world, there would only be one codec for everything and it would work perfectly across all devices regardless of origin, operating system or playback platform. Someday!

Common audio and video codecs include those listed below (a small explanation is included for each).

DivX

These file types show up very frequently; you may recognize the file extension .avi as it is an extremely popular container for video; avi files usually contain video encoded using DivX. The DivX codec is available for free download (*a quick search on the internet will likely yield dozens of locations where you can attain it, if need be) and enables video playback in popular players such as Windows Media Player and Apple QuickTime.

Xvid

Very similar to DivX, these are also usually found in an AVI container; the video file you want to watch may end with .avi, but the content was actually encoded with Xvid. As with DivX, the Xvid codec is readily available for free download with a quick search. The differences between the two are thus: Xvid is actually the technically superior option of the two (*reason: it allows for much faster data transmission and more efficient storage), but it isn’t quite as common as DivX.

MPEG-2

MPEG-2 is a widely used codec for transmitting over-the-air television broadcasts, satellite television signals and movies on DVD discs. The MPEG codec was invented by the The Moving Pictures Expert Group, hence the name mpeg. MPEG-2 was developed some time ago and as such it is slowly becoming antiquated due to the amount of disc storage space it requires; there are codecs available today which retain the same level of quality while using less space. Still, MPEG-2 is the standard for DVDs, and DVD’s are still a very popular type of media amongst consumers.

H.264

The latest and some would say greatest compression standard, H.264 is poised to become the industry standard in the near future. The reason for this is that it offers the most efficient compression with almost zero image loss or degradation, it can compress source files by up to 80% which means that less bandwidth or storage space is required. It is also expected to infiltrate the still camera market since the technology is capable of compressing large picture files and data bit rates without image quality being compromised. Already in use on most hand-held devices, it is quickly gaining recognition and acceptance by consumers.

MP3

First became known to the public in 1995, today MP3 is not only a generally accepted format by users it’s basically the way most people listen to music. The name stems from the technology – MPEG 1/2 Layer 3 = MP3. While it is a lossy codec (for music purists, perhaps look into FLAC encoded music as it is the ‘go-to’ lossless audio format for many), it can be encoded at high bit-rates enabling playback of music that is missing some miniscule details that generally aren’t audible to most listeners. It is also universally accepted and recognized everywhere.

AAC

The initials stand for ‘Advanced Audio Coding’. While AAC is a lossy codec, like the similar MP3 codec, it is capable of reproducing superior sound quality at similar bit rates when compared to MP3. For these reasons it was also initially deemed to be the successor to MP3. It is the compression standard for most Apple products as well as various gaming platforms (PlayStation 3, Nintendo DSi) as well as YouTube.

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