BASSmix

BASS_Mixer_StreamCreate

Creates a mixer stream.

HSTREAM BASS_Mixer_StreamCreate(
    DWORD freq,
    DWORD chans,
    DWORD flags
);

Parameters

freq

The sample rate of the mixer output.

chans

The number of channels... 1 = mono, 2 = stereo, 4 = quadraphonic, 6 = 5.1, 8 = 7.1.

flags

Any combination of these flags.

BASS_SAMPLE_8BITS	Produce 8-bit output. If neither this or the BASS_SAMPLE_FLOAT flags are specified, then the stream is 16-bit.
BASS_SAMPLE_FLOAT	Produce 32-bit floating-point output. WDM drivers or the BASS_STREAM_DECODE flag are required to use this flag in Windows. See Floating-point channels for more info.
BASS_SAMPLE_SOFTWARE	Force the stream to not use hardware mixing. Note this only applies to playback of the mixer's output; the mixing of the source channels is always performed by BASSmix.
BASS_SAMPLE_3D	Use 3D functionality. This requires that the BASS_DEVICE_3D flag was specified when calling BASS_Init, and the stream must be mono (chans=1). The SPEAKER flags can not be used together with this flag.
BASS_SAMPLE_FX	Enable the old implementation of DirectX 8 effects. See the DX8 effect implementations section for details. Use BASS_ChannelSetFX to add effects to the stream.
BASS_STREAM_AUTOFREE	Automatically free the stream when playback ends.
BASS_STREAM_DECODE	Mix the sample data, without playing it. Use BASS_ChannelGetData to retrieve the mixed sample data. The BASS_SAMPLE_3D, BASS_STREAM_AUTOFREE and SPEAKER flags can not be used together with this flag. The BASS_SAMPLE_SOFTWARE, BASS_SAMPLE_FX and BASS_MIXER_RESUME flags are also ignored.
BASS_MIXER_END	End the stream when there are no active (including stalled) source channels, else it is never-ending.
BASS_MIXER_NONSTOP	Do not stop producing output when there are no active source channels, else it will be stalled until there are active sources.
BASS_MIXER_POSEX	Keep a record of the source positions, making it possible to account for output latency when retrieving a source position. How far back the position record goes is determined by the BASS_CONFIG_MIXER_POSEX config option. If this flag is not used and neither is the BASS_STREAM_DECODE flag, then the mixer will automatically have a position record of equal length to the BASS_CONFIG_BUFFER setting.
BASS_MIXER_RESUME	When stalled, resume the mixer immediately upon a source being added or unpaused, else it will be resumed at the next update cycle.
BASS_SPEAKER_xxx	Speaker assignment flags. These flags have no effect when the stream is more than stereo.

Return value

If successful, the new stream's handle is returned, else 0 is returned. Use BASS_ErrorGetCode to get the error code.

Error codes

BASS_ERROR_INIT	BASS_Init has not been successfully called.
BASS_ERROR_NOTAVAIL	Only decoding channels (BASS_STREAM_DECODE) are allowed when using the "no sound" device. The BASS_STREAM_AUTOFREE flag is also unavailable to decoding channels.
BASS_ERROR_FORMAT	The sample format is not supported by the device/drivers. If the stream is more than stereo or the BASS_SAMPLE_FLOAT flag is used, it could be that they are not supported.
BASS_ERROR_SPEAKER	The specified SPEAKER flags are invalid. The device/drivers do not support them, they are attempting to assign a stereo stream to a mono speaker or 3D functionality is enabled.
BASS_ERROR_MEM	There is insufficient memory.
BASS_ERROR_NO3D	Could not initialize 3D support.
BASS_ERROR_UNKNOWN	Some other mystery problem!

Remarks

Source channels are "plugged" into a mixer using the BASS_Mixer_StreamAddChannel or BASS_Mixer_StreamAddChannelEx functions, and "unplugged" using the BASS_Mixer_ChannelRemove function. Sources can be added and removed at any time, so a mixer does not have a predetermined length and BASS_ChannelGetLength is not applicable. Likewise, seeking is not possible, except to position 0, as described below.

If the mixer output is being played (it is not a decoding channel), then there will be some delay in the effect of adding/removing source channels or changing their attributes being heard. This latency can be reduced by making use of the BASS_CONFIG_BUFFER and BASS_CONFIG_UPDATEPERIOD config options. The playback buffer can be flushed by calling BASS_ChannelPlay (restart = TRUE) or BASS_ChannelSetPosition (pos = 0). That can also be done to restart a mixer that has ended.

Unless the BASS_MIXER_END flag is specified, a mixer stream will never end. When there are no sources (or the sources have ended/stalled), it will produce no output until there is an active source. That is unless the BASS_MIXER_NONSTOP flag is used, in which case it will produce silent output while there are no active sources. The BASS_MIXER_END and BASS_MIXER_NONSTOP flags can be toggled at any time, using BASS_ChannelFlags.

Besides mixing channels, a mixer stream can be used for sample rate conversion. In that case the freq parameter would be set to the new sample rate, and the source channel's attributes would be left at their defaults. A mixer stream can also be used to downmix, upmix and generally rearrange channels, using the matrix mixing features.

Platform-specific

Away from Windows, all mixing is done in software (by BASS), so the BASS_SAMPLE_SOFTWARE flag is unnecessary. The BASS_SAMPLE_FX flag is also ignored.