Codecs: frequently asked questions

A codec compresses or decompresses media files such as songs or videos. Windows Media Player and other apps use codecs to play and create media files.

A codec can consist of two parts: an encoder that compresses the media file (encoding), and a decoder that decompresses the file (decoding). Some codecs include both parts, and other codecs only include one of them.

1.  On the Help menu in Windows Media Player, select About Windows Media Player.
   If you can't see the Help menu, select Organize, select Layout, and then select Show menu bar.
2. In the About Windows Media Player dialog box, select Technical Support Information.
   Your web browser will open a page that includes a lot of detailed info about the related binary files, codecs, filters, plug-ins, and services installed on your PC. You might be able to use this info to help troubleshoot problems.

There are hundreds of audio and video codecs in use today. Some have been created by Microsoft, but the vast majority of codecs have been created by other companies, organizations, or individuals. By default, the Windows operating system and the Player include a number of the most popular codecs, such as Windows Media Audio, Windows Media Video, and MP3.

There might be times, however, when you want to play content that was compressed with a codec that Windows or the Player doesn't include by default. In many cases, you can download the necessary codec from the web for free or for a fee. And, in some cases, the Player can automatically use the codecs installed by other digital media playback and creation programs on your computer.

If you get a message that says that your computer is missing a codec, you are probably trying to play, burn, or sync a file that was compressed by using a codec that Windows or the Player doesn't include by default.

If you know the name of the codec or its ID (known as a FourCC identifier for video codecs or a WaveFormat identifier for audio codecs), try searching the Internet. You can often go to a codec manufacturer's website to download the most recent version of a codec.

A DVD decoder is another name for an MPEG-2 decoder. The content on DVD-Video discs is encoded in the MPEG-2 format, as is the content in DVR-MS files (Microsoft Recorded TV Shows) and some AVI files. To play these items in the Player, you need a compatible DVD decoder installed on your computer.

If your computer has a DVD drive, it probably already has a DVD decoder installed on it. However, if you encounter an error message that indicates that you are missing a compatible DVD decoder, select the Web Help button in the error message dialog box to determine how to obtain one.

This might happen if your computer at work doesn't have the same codecs installed on it that your computer at home does.

For example, if you are trying to play a DVD-Video disc or DVR-MS file on your computer at work and that computer doesn't have a DVD decoder installed on it, you won't be able to play that item until you install a compatible DVD decoder on your work computer.

Note that your system administrator at work might use Group Policy to prevent you from installing new codecs.

Codecs can be written for 32-bit or 64-bit operating systems. If you are running a 64-bit version of Windows, you need to install 64-bit codecs. If you install a 32-bit codec on a 64-bit operating system, for example, the Player might not be able to play any files that require that codec.

Note that many older codecs are only available in 32-bit versions. If the codec provider does not specify whether its codec is 32-bit or 64-bit, the codec is likely 32-bit. For more information, contact the codec provider.

There isn't a way to determine the codec used to compress a file with absolute certainty, but the following are your best options:

• To determine what codec was used with a specific file, play the file in the Player, if possible. While the file is playing, right-click the file in the library, and then select Properties. On the File tab, look at the Audio codec and Video codec sections.
• Use a non-Microsoft codec identification tool. Several are available on the Internet.

You might be able to tell the format of a file by looking at the file name extension (such as .wma, .wmv, .mp3, or .avi). However, there are limits to this approach. Many programs create files with custom file extensions. And it's possible for anyone to rename a file without changing the file's format. A file with the extension .mpg or .dvr-ms, for instance, is usually just an AVI file that has been compressed by using some version of an MPEG video codec.