This article was previously published under Q289196
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When you play a DVD movie under Windows 2000 (Service Pack 1 or earlier), using a sound card equipped with a digital output, the Dolby Digital 5.1-channel bitstream (also known as AC-3) will not be sent through the digital output of the sound card.
This occurs whether the digital output uses a coaxial "RCA"-type S/PDIF (Sony/Philips Digital Interface Format) jack, or an optical (Toslink) connector. This also applies to DVDs using a DTS (Digital Theater Sound) 5.1-channel soundtrack.
Digital 5.1-channel output from the sound card is normally used in conjunction with an external digital decoder such as a home theater audio receiver equipped with Dolby Digital/DTS decoding.
Stereo audio played through the computer speakers is not affected.
This behavior occurs because the Windows Driver Model (WDM) audio device driver Wdmaud.drv does not support non-Pulse Code Modulation (PCM) WAV formats. Wdmaud interacts with Kmixer.sys, the kernel audio mixer, which supports only PCM, but software DVD players require the use of non-PCM formats to play content like AC3 audio.
To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in theMicrosoft Knowledge Base:
260910 How to Obtain the Latest Windows 2000 Service Pack
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.
This problem was first corrected in Windows 2000 Service Pack 2.
Depending on the design of the sound card drivers, you may also need to obtain a new driver revision from your sound card vendor in order to utilize the multichannel digital output capability which is enabled by Service Pack 2.
Your DVD playback/decoder software must also support passing the digital output to the sound card's digital output.