What is a Codec Anyway?

If you work at all with digital video, you’re bound to run into issues of media compatibility. What makes a video incompatible? Will it work in InqScribe? It’s a complicated subject. In this post, we’ll explain a few key terms that should help you understand how digital video works (and sometimes, how it doesn’t work).


Codec stands for coder/decoder, and it does just that. Raw video tends to take up large amounts of storage, and codecs allow us to shrink down the file size, usually without losing too much quality. Codecs achieve this by taking the raw video data and encoding it into a shorthand. Once encoded, codecs also play a role in decoding this shorthand.

Note that codecs are independent of a video’s file extension. So, .mp4, .avi, .mov, etc. are not codecs. A .mp4 file could use a H.264/AVC or MPEG-4 Part 2 codec, for example. You can see which codecs are supported by QuickTime via Apple’s support page here. To check which codecs you have available in Windows Media Player, follow Microsoft’s directions here (use drop-down bar on right to select your version of Windows).

Although some are more popular than others, there are dozens of different codecs out there. Since each uses a unique coding language, it’s important to use codecs that are compatible with your workflow (and that you have access to- some codecs are proprietary). What should you do if you come across an incompatible codec? Transcode! More on that in a bit…


QuickTime "movie could not be opened" message
Look familiar?

As its name suggests, a container file packages compressed video data. Containers identify and sort out codecs, which are the ones doing the actual compressing. Most common video containers are compatible with multiple codecs, so don’t assume one container is always going to have the same codec.

Chances are, you’re more familiar with containers than you are with codecs. They’re more visible because the file extension is often associated with the container. A file with the name “Sample.mp4” has a file extension of “.mp4”, which indicates the MP4 container. Other examples of containers include AVI, MPEG-2, FLV, and RM to name a few.

In addition to a file’s codec, programs such as QuickTime and Windows Media Player will have their own specs for which containers they support. So, to drive this home: just because you have a compatible container for your video file, it doesn’t mean you have a compatible codec. And vise-versa.


To transcode is to convert from one encoding to another. When you transcode a file, you are essentially changing a video’s codec or its container, perhaps both. The terms “transcoding” and “converting” are generally used interchangeably.

It’s worth noting that transcoding a file will result in some loss of quality. The extent of this may or may not be noticeable.

If you’re interested in transcoding, check out our blog post on Media Conversion Tools for more information.


To “mux” a file is to combine multiple channels into one. When referring to video files, these channels are typically audio, video, and/or subtitle tracks. Muxing is useful when compiling several of these tracks into one output, such as when you’re creating a DVD or Blu-ray disk.

Since not all media player can process muxed files, you might not always want a file to be muxed. This is when demuxing comes into play.


To demux a file is to extract the individual tracks back into their separate channels. Demuxing is useful when you come across an unsupported muxed file.

Since transcoding will rewrite a file’s video and audio data, it can actually be used to demux a file. So, when in doubt, transcoding can solve several different problems associated with incompatibility.

Understanding these terms and concepts should equip you to deal with incompatible media. And remember, if you’re ever having trouble getting InqScribe to recognize your media files, just send an email to support@inqscribe.com.

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