Codecs, Containers and Players

Is it a Quicktime file, or an MOV? Is it an h.264 file, or is it an F4V? If I have a file in i-Tunes, it must be an MP3 or MP4, right? If you spend any time working with video files, you know what I’m talking about. Its just plain confusing.

Lets start with the codecs. Codec is short for “compressor – decompressor” or “coder-decoder”. Typically a codec is either proprietary (owned by the patent holder) or open source. When working with video, we will typically use an audio codec and a video codec, and combine both into the same container. When working with a non-linear editor such as Final Cut Pro or Premiere, you’ll see the available output codecs presented in a dropdown box in the related area (audio settings and video settings). Here is a short list of some of the more popular codecs.

Example Video codecs: VP6, h.264, Sorenson Spark, Windows Media Video, MPEG 2, RealVideo – lots of flavors of each.
Example Audio codecs: AAC, MP3, AC3, Windows Media Audio, MPEG 2 audio layer, FLAC

If you’re preparing your video for the web, you will find today’s most propular codecs are VP6 (also known as Flash video) and h.264 for video, and AAC or MP3 for audio. Typically you will pair AAC audio with h.264 and MP3 with VP6.

Now lets look at containers. This is essentially the file extension, such as WMV, FLV, MOV, AVI or MP4. These file extensions are used to associate the file with a particular software program (or player). For instance, the MOV format is most often associated with the Quicktime player. The WMV format is most often associated with the Windows Media Player. When you click an MOV, it typically opens and plays in the Quicktime player – as does clicking the WMV opens up the Windows Media Player and plays the file. On my work computer, when I double-click an MP4 it opens up and begins playing in Quicktime. On my home computer, when I double-click an MP4 it opens up and begins playing in iTunes. You can change the program associated with a particular extension (in Windows) by clicking Control Panel –> Tools –> Folder Options –> File Types, identify the type you want to change, highlight it and click “Change” in the “Opens with” area.

You can use some codecs in a variety of containers. For instance, the h.264 codec can be used in the MP4, M4V, F4V, and MPEG4 containers. The MP3 audio codec can be used in FLV or MP3 containers.

Then you have the players. Once again, depending how you have the “Open With” settings configured, you could click an AVI and it could open the file up using Quicktime, or Windows Media Player, Real Player or just about any other audio player such as Winamp.

So when someone tells you they have a Quicktime file, what does that really mean? Is it because it opens up and plays with Quicktime, or maybe because it has an extension that is associated with Quicktime (.mov for instance)?

Understanding codecs, containers and players is essential to understanding computer or web-based video from a technical perspective. It sure makes troubleshooting quality or playback issues much easier. With so many websites offering User Uploads, this type of general knowledge comes in very handy.

A few good links if you’re interested in learning more.

Wikipedia: Video Codecs
Wikipedia: Audio Codecs
Wikipedia: Open Source Codecs and Containers:
Moving Pictures Experts Group:
Great article on Video Encoding Fundamentals & H.264:

Posted by Chuck Ebbets   @   17 November 2009

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