|
|
On WDM drivers, DirectSound buffers support WAV formats that have more than two output channels, for speaker configurations such as 5.1, which has speakers at the front left, front center, front right, back left, and back right, plus a low-frequency enhancer. They also support formats with sample resolutions of greater than 16 bits.
Such formats can be described by a WAVEFORMATEXTENSIBLE structure. This structure is an extension of WAVEFORMATEX that configures the extra bytes specified by the WAVEFORMATEX.cbSize. A WAVEFORMATEXTENSIBLE structure can be cast as WAVEFORMATEX wherever the latter is expected, as for example in the DSBUFFERDESC structure. DirectSound recognizes multichannel and high-resolution formats by the WAVE_FORMAT_EXTENSIBLE tag in WAVEFORMATEX.wFormatTag.
You do not have to use the WAVEFORMATEXTENSIBLE type definition in your application in order to play multichannel or high-resolution files. You need only parse the file header correctly into a WAVEFORMATEX structure that contains the extra bytes specified by cbSize. For an example of how to allocate the WAVEFORMATEX structure, see the CWaveFile::ReadMMIO function in the DirectSound samples.
If the system is configured for fewer physical speakers than the number of channels specified in a multichannel WAV file, the audio data is mixed appropriately and output to the existing speakers.
DirectSound does not support effects or 3D processing on buffers in a multichannel format. An attempt to create a buffer with the DSBCAPS_CTRL3D or DSBCAPS_CTRLFX flag and a multichannel WAV format will fail.
For more information on multichannel WAV formats, see Multiple Channel Audio Data and WAVE Files, available at www.microsoft.com.