Here are answers to some common questions about codecs.

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What is a codec?

A codec is software that is used to compress or decompress a digital media file, such as a song or video. Windows Media Player and other programs use codecs to play and create digital media files.

A codec can consist of two components: an encoder and a decoder. The encoder performs the compression (encoding) function and the decoder performs the decompression (decoding) function. Some codecs include both of these components and some codecs only include one of them.

For example, when you rip a song from an audio CD to your computer, the Player uses the Windows Media Audio codec by default to compress the song into a compact WMA file. When you play that WMA file (or any WMA file that might be streamed from a website), the Player uses the Windows Media Audio codec to decompress the file so the music can be played through your speakers.

Which codecs are included with the Player?

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.

Why do I get a message that says my computer is missing a codec?

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.

How do I find a codec?

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.

Warning

  • Use caution when installing codecs that you find on the Internet, particularly some of the free codec packs that claim to include codecs from a wide variety of companies or organizations. Incompatibilities are known to exist with some of the components in these codec packs that can cause serious playback issues in the Player and other players, lead to system corruption, and make it difficult for Microsoft Support to diagnose and troubleshoot playback issues. For these reasons, we strongly discourage you from installing these codec packs, and recommend that you remove them if you have installed them and you are having problems with the Player. Install only codecs, filters, or plug-ins from trusted, authorized sources, such as the website of the official supplier. Even then, use caution: some codec suppliers offer minimal customer support. Before installing any digital media components, set a system restore point. The restore point enables you to return to your original system configuration, if necessary.

What is a DVD decoder?

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, click the Web Help button on the error message dialog box to determine how to obtain one.

Why can't I play a file at work that I can play at home?

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.

I installed a missing codec, but I still can't play the file. Why?

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.

How do I tell which codecs are installed on my computer?

If you need to see a list of the Windows Media Player components and codecs installed on your computer, do the following:

  1. On the Help menu, click About Windows Media Player.

    If the Help menu is not visible, click Organize, point to Layout, and then select Show menu bar.

  2. On the About Windows Media Player dialog box, click Technical Support Information.

    Your web browser will open a page that includes information about the related binary files, codecs, filters, plug-ins, and services installed on your computer. A technical support person might be able to use this detailed information to help you troubleshoot problems on your computer.

How do I tell which codec was used to compress a file and what format a file is in?

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 click 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.

Are codecs and file formats the same?

No, although it can be confusing because they sometimes have the same name. You can think of a file format as a type of container. Inside the container is data that has been compressed by using a particular codec. For example, a file format such as Windows Media Audio contains data that is compressed by using the Windows Media Audio codec. However, a file format such as Audio Video Interleaved (AVI) can contain data that is compressed by any of a number of different codecs, including the MPEG-2, DivX, or XviD codecs. AVI files can also contain data that is not compressed by any codec. Consequently, you might be able to play some AVI files and not others, depending on which codecs were used to compress the file and which codecs you have installed on your computer. For the same reason, you also might be able to play the audio portion of an AVI file, but not the video portion.