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Decoder Volume Control

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[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

Applications control audio volume through the IBasicAudio interface. An IBasicAudio interface handler is provided for KSProxy. For a decoder to handle the volume commands from KSProxy, it must add several registry keys in its setup script and support the KSPROPSETID_Wave property set.

Create some new registry keys for the driver:

HKLM\SYSTEM\
  CurrentControlSet\Control
    DeviceClasses
      (decoder guid, eg 2721AE....)
        (Pnp id, eg ##?#VDGENDEV#...)
          #GLOBAL
            Device Parameters
              CLSID      REG_SZ   {17CCA...}
                FriendlyName   REG_SZ   WDM DVD Driver
                  Interfaces <--- create this key
                  {b9f8ac3e-0f71-11d2-b72c-00c04fb6bd3d} // Create this key.
    MediaInterfaces
      {b9f8ac3e-0f71-11d2-b72c-00c04fb6bd3d} // Create this key.
        (default)  REG_SZ   'KsProxy IBasicAudio handler' // Set this value.
        IID        REG_SZ   56 a8 68 b3 0a d4 11 ce b0 3a 00 20 af 0b a7 70 
                            // Create this key.

To implement volume control, the driver also must support KSPROPSETID_Wave, along with KsProperty.Id = KSPROPERTY_WAVE_VOLUME. This property is passed to the driver through the IKsPropertySet::Get and IKsPropertySet::Set methods. The LeftAttenuation and RightAttentuation fields specify the left/right speaker volumes as linear values from 0x0000 to 0xffff.

Decoder Interfaces and Specifications