Audio Mixer: Technical Specs

Revision as of 18:26, 25 January 2011

Audio Mixer DirectShow specs.

Audio mixer is a standard DirectShow filter.

Number of input pins = 2 for stereo and mono modes and from 1 to 64 for custom mode (new pin will be added after connection of all free input pins).

Number of output pins = 1 for stereo and mono modes and from 1 to 64 for custom mode (new pin will be added after connection of all free output pins).

Number of bits per mono audio sample for any input or output: from 8 to 32

Input/output media type:

 majortype:
   MEDIATYPE_Audio
 subtype:
   MEDIASUBTYPE_PCM
 formattype:
   FORMAT_WaveFormatEx
 cbFormat, pbFormat:
   WAVEFORMATEX struct (wFormatTag = WAVE_FORMAT_PCM) for nChannels = 1 or 2 only
   WAVEFORMATEXTENSIBLE struct (Format.wFormatTag = WAVE_FORMAT_EXTENSIBLE)

Parameters of format:

WAVEFORMATEX::nSamplesPerSec and WAVEFORMATEX::wBitsPerSample: the same for all inputs/outputs.

WAVEFORMATEX::nChannels from 1 to 32. Can be different for different input/output pins.

Any channel(s) of any input pin(s) can be mixed with any other channel(s) of same or other input pin(s). Mixing coefficients can be changed in play time also (without graph stop).

Notes:

• All input frequencies and bits per mono samples should be identical (resampling not implemented in current version).

• Only 8 or 16 bits per mono audio sample supported in current version

• After start of graph the media type of output pins cannot be changed.

The filter has IMLAudioMixer interface and property page for set/get parameters of mixing (Input/channel -> Output/channel) and other parameters.