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Uncompressed audio and video content can consume a lot of bandwidth when streaming or create large files. By compressing the content, it can be broadcast over common Internet bandwidths or saved to a Windows Media file of a reasonable size. You can compress content by applying compression algorithms to the data, taking into account the desired output quality and available bandwidth. Before the content is played, it is decompressed by using decompression algorithms. These compression and decompression algorithms are called codecs. The following table provides more detailed information about the codecs available in Windows Media Encoder.
| Codec | Description |
| Windows Media Audio 9 Professional | Provides a full surround sound experience and dynamic range control. Intelligently folds down multichannel audio to 2 (stereo) or 1 (mono), depending on the speaker configuration of the playback device. Intended for data rates of 128 to 768 Kbps. |
| Windows Media Audio 9 Lossless | Provides lossless encoding of audio content. Supports multichannel audio encoding and dynamic range control. |
| Windows Media Audio 9 | Provides a 20 percent improvement in compression over the Windows Media Audio 8 codec. Supports VBR audio encoding. |
| Windows Media Audio 9 Voice | Offers superior quality for audio content with a voice emphasis. Provides for mixed-mode encoding of voice and music. Intended for playback at bit rates at 20 Kbps or lower. |
| Windows Media Video 9 | Creates high-quality video for streaming, download-and-play, and physical format delivery scenarios. Provides a 15 to 50 percent improvement in compression over the Windows Media Video 8.1 codec, with the more significant improvement occurring at higher bit rates. Enables playback of interlaced content on televisions and set-top boxes. |
| Windows Media Video 8.1 | Supports a wide variety of network bandwidths. Deinterlaces interlaced content before encoding. |
| Windows Media Video 7 | Enables users of Windows Media Player 7 to view encoded video content without first having to download the latest codecs. Best choice when the encoding computer cannot support the performance requirements of the newer Windows Media Video codecs. |
| Windows Media Video 9 Screen | Provides improved handling of shaded images, screen motion, and scrolling for screen captures. Supports one-pass CBR and VBR encoding with no frame dropping. This codec is fully optimized for both streaming and download-and-play scenarios. |
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