[wdmaudiodev] AC3 support in KMixer

  • From: "Van Mieghem, Dirk" <dvm@xxxxxxxx>
  • To: "'wdmaudiodev@xxxxxxxxxxxxx'" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Sun, 13 Oct 2002 22:05:54 +0200

I had some problems adding AC3 support to a WDM/KS driver. I folowed the
non-PCM document written by Microsoft but only a waveout device would pass
KSDATAFORMAT_SUBTYPE_DOLBY_AC3_SPDIF to the driver. An AC3 decoder graph
constructed with a waveout device would play such a stream without an

The only problem is that Microsoft is fading the classic wave API away in
favor of DirectSound. I don't understand why as I don't see a single
advantage in using DS. Anyway, DirectSound seems to pass non-PCM streams to
the driver only if there's a topology port. I don't grasp the link between
AC3 and topology but there has to be a topo connection or you don't get
non-audio data.

Well, it works now but the performance is extremely bad. The directsound
renderer inserts breaks and silence whenever there's some activity on the
system, impossible to play a video with AC3, sync is completely lost within
seconds. Anyone seen similar behavior and more important, a solution maybe?


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