BassMixBASS_Mixer_StreamCreate Method

[DllImportAttribute("bassmix")]
public static int BASS_Mixer_StreamCreate(
	int freq,
	int chans,
	BASSFlag flags
)

<DllImportAttribute("bassmix">]
Public Shared Function BASS_Mixer_StreamCreate ( 
	freq As Integer,
	chans As Integer,
	flags As BASSFlag
) As Integer

Parameters

freq

Type: SystemInt32
The sample rate of the mixer output (e.g. 44100).

chans

Type: SystemInt32
The number of channels... 1 = mono, 2 = stereo, 4 = quadraphonic, 6 = 5.1, 8 = 7.1. More than stereo requires WDM drivers (or the BASS_STREAM_DECODE flag) in Windows, and the SPEAKER flags are ignored.

flags

Type: Un4seen.BassBASSFlag
Any combination of these flags (see BASSFlag):

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_3D	Use 3D functionality. This is ignored if BASS_DEVICE_3D wasn't specified when calling BASS_Init(Int32, Int32, BASSInit, IntPtr, IntPtr). 3D streams must be mono (chans=1). The SPEAKER flags can not be used together with this flag.
BASS_STREAM_AUTOFREE	Automatically free the stream's resources when BASS_ChannelStop(Int32) (or BASS_Stop) is called.
BASS_STREAM_DECODE	Decode the sample data, without outputting it. Use BASS_ChannelGetData(Int32, IntPtr, Int32) to retrieve decoded sample data. The BASS_SAMPLE_SOFTWARE, BASS_SAMPLE_3D, BASS_SAMPLE_FX, BASS_STREAM_AUTOFREE and SPEAKER flags can not be used together with this flag.
BASS_MIXER_END	End the stream when there are no active (including stalled) source channels, else it's never-ending.
BASS_MIXER_NONSTOP	Don't stop producing output when there are no active source channels, else it will be stalled until there are active sources.
BASS_MIXER_NOSPEAKER	Ignore speaker arrangement. This flag tells BASSmix to not make any special consideration for speaker arrangements when mixing multi-channel content or using the SPEAKER flags, eg. swapping the CENLFE and REAR speaker channels in 5/7.1 speaker output. This flag should be used with plain multi-channel (rather than 5/7.1) output.
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_QUEUE	Play the sources one at a time, in the order that they were added.
BASS_MIXER_RESUME	When stalled, resume the mixer immediately upon a new or unpaused source, else it will be resumed at the next update cycle.
BASS_SPEAKER_xxx	Speaker assignment flags.

Return Value

Source channels are added into a mixer using the BASS_Mixer_StreamAddChannel(Int32, Int32, BASSFlag) or BASS_Mixer_StreamAddChannelEx(Int32, Int32, BASSFlag, Int64, Int64) functions, and removed using the BASS_Mixer_ChannelRemove(Int32) function. Sources can be added and removed at any time, so a mixer does not have a predetermined length and BASS_ChannelGetLength(Int32, BASSMode) 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(Int32, Boolean) (restart = TRUE) or BASS_ChannelSetPosition(Int32, Int64, BASSMode) (pos = 0). That can also be done to restart a mixer that has ended.

Seeking in a mix via BASS_ChannelSetPosition(Int32, Int64, BASSMode) directly is not possible, but seeking can be implemented by setting the position of each source to where it would be at the seek position, and then flushing the mixer's playback buffer (see above) if required.

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'll produce no output until there's an active source. That's 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(Int32, BASSFlag, BASSFlag).

A queued mixer, with the BASS_MIXER_QUEUE flag set, will play its sources one after another in the order that they were added, without a gap unless a delay is specified with BASS_Mixer_StreamAddChannelEx(Int32, Int32, BASSFlag, Int64, Int64). After a source has been played, it will be removed from the mixer. Queueing can be enabled or disabled at any time using BASS_ChannelFlags(Int32, BASSFlag, BASSFlag). If it is disabled that way then all currently queued sources will start immediately, and if it is enabled then any current sources will continue to play normally and newly queued sources will start when the current ones have all ended. A BASS_SYNC_MIXER_QUEUE sync can be set to be notified whenever a source is dequeued.

Besides mixing channels, a mixer stream can be used as a resampler. In that case the freq parameter would be set 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.

By default, a mixer is single-threaded, meaning it will process its sources one at a time. When there are multiple sources and multiple CPU cores available, it may be advantageous to enable multiple threads via the BASS_ATTRIB_MIXER_THREADS setting.

// this will be the final mixer output stream being played
int mixer = BassMix.BASS_Mixer_StreamCreate(44100, 2, BASSFlag.BASS_SAMPLE_FLOAT );
// now we need some channels to plug them in...create two decoding sources
int streamA = Bass.BASS_StreamCreateFile("testA.mp3", 0, 0, 
                   BASSFlag.BASS_STREAM_DECODE | BASSFlag.BASS_SAMPLE_FLOAT);
int streamB = Bass.BASS_StreamCreateFile("testB.mp3", 0, 0, 
                   BASSFlag.BASS_STREAM_DECODE | BASSFlag.BASS_SAMPLE_FLOAT);
// finally we plug them into the mixer (no downmix, since we assume the sources to be stereo)
bool okA = BassMix.BASS_Mixer_StreamAddChannel(mixer, streamA, BASSFlag.BASS_DEFAULT);
bool okB = BassMix.BASS_Mixer_StreamAddChannel(mixer, streamB, BASSFlag.BASS_DEFAULT);
// and play it...
Bass.BASS_ChannelPlay(mixer, false);

' this will be the final mixer output stream being played
Dim mixer As Integer = BassMix.BASS_Mixer_StreamCreate(44100, 2, BASSFlag.BASS_SAMPLE_FLOAT)
' now we need some channels to plug them in...create two decoding sources
Dim streamA As Integer = Bass.BASS_StreamCreateFile("testA.mp3", 0, 0, 
                              BASSFlag.BASS_STREAM_DECODE Or BASSFlag.BASS_SAMPLE_FLOAT)
Dim streamB As Integer = Bass.BASS_StreamCreateFile("testB.mp3", 0, 0, 
                              BASSFlag.BASS_STREAM_DECODE Or BASSFlag.BASS_SAMPLE_FLOAT)
' finally we plug them into the mixer (no downmix, since we assume the sources to be stereo)
Dim okA As Boolean = BassMix.BASS_Mixer_StreamAddChannel(mixer, streamA, BASSFlag.BASS_DEFAULT)
Dim okB As Boolean = BassMix.BASS_Mixer_StreamAddChannel(mixer, streamB, BASSFlag.BASS_DEFAULT)
' and play it...
Bass.BASS_ChannelPlay(mixer, False)

Reference