Поделиться через

IAudioEndpointVolume::GetVolumeRange

  • Статья
Previous Next

IAudioEndpointVolume::GetVolumeRange

The GetVolumeRange method gets the volume range, in decibels, of the audio stream that enters or leaves the audio endpoint device.

HRESULT GetVolumeRange(
  float  *pfLevelMinDB,
  float  *pfLevelMaxDB,
  float  *pfVolumeIncrementDB
);

Parameters

pfLevelMinDB

[out]  Pointer to the minimum volume level. This parameter points to a float variable into which the method writes the minimum volume level in decibels. This value remains constant for the lifetime of the IAudioEndpointVolume interface instance.

pfLevelMaxDB

[out]  Pointer to the maximum volume level. This parameter points to a float variable into which the method writes the maximum volume level in decibels. This value remains constant for the lifetime of the IAudioEndpointVolume interface instance.

pfVolumeIncrementDB

[out]  Pointer to the volume increment. This parameter points to a float variable into which the method writes the volume increment in decibels. This increment remains constant for the lifetime of the IAudioEndpointVolume interface instance.

Return Value

If the method succeeds, it returns S_OK. If it fails, possible return codes include, but are not limited to, the values shown in the following table.

Return code Description
E_POINTER Parameter pfLevelMinDB, pfLevelMaxDB, or pfVolumeIncrementDB is NULL.

Remarks

The volume range from vmin = *pfLevelMinDB to vmax = *pfLevelMaxDB is divided into n uniform intervals of size vinc = *pfVolumeIncrementDB, where

n = (vmax – vmin) / vinc.

The values vmin, vmax, and vinc are measured in decibels. The client can set the volume level to one of n + 1 discrete values in the range from vmin to vmax.

The IAudioEndpointVolume::SetChannelVolumeLevel and IAudioEndpointVolume::SetMasterVolumeLevel methods accept only volume levels in the range from vmin to vmax. If the caller specifies a volume level outside of this range, the method fails and returns E_INVALIDARG. If the caller specifies a volume level that falls between two steps in the volume range, the method sets the endpoint volume level to the step that lies closest to the requested volume level and returns S_OK. However, a subsequent call to IAudioEndpointVolume::GetChannelVolumeLevel or IAudioEndpointVolume::GetMasterVolumeLevel retrieves the volume level requested by the previous call to SetChannelVolumeLevel or SetMasterVolumeLevel, not the step value.

If the volume control is implemented in hardware, GetVolumeRange describes the range and granularity of the hardware volume settings. In contrast, the steps that are reported by the IEndpointVolume::GetVolumeStepInfo method correspond to points on an audio-tapered curve that are calculated in software by the IEndpointVolume::VolumeStepDown and IEndpointVolume::VolumeStepUp methods. Either method first calculates the idealized volume level that corresponds to the next point on the curve. Next, the method selects the hardware volume setting that is the best approximation to the idealized level. For more information about audio-tapered curves, see Audio-Tapered Volume Controls.

Requirements

Client: Windows Vista

Header: Include Endpointvolume.h.

See Also

Previous Next