BassWasapiBASS_WASAPI_Init Method (Int32, Int32, Int32, BASSWASAPIInit, Single, Single, WASAPIPROC, IntPtr)

[DllImportAttribute("basswasapi")]
public static bool BASS_WASAPI_Init(
	int device,
	int freq,
	int chans,
	BASSWASAPIInit flags,
	float buffer,
	float period,
	WASAPIPROC proc,
	IntPtr user
)

<DllImportAttribute("basswasapi">]
Public Shared Function BASS_WASAPI_Init ( 
	device As Integer,
	freq As Integer,
	chans As Integer,
	flags As BASSWASAPIInit,
	buffer As Single,
	period As Single,
	proc As WASAPIPROC,
	user As IntPtr
) As Boolean

Parameters

device

Type: SystemInt32
The device to use... 0 = first device, -1 = default output device, -2 = default input device, -3 = default loopback input device. BASS_WASAPI_GetDeviceInfo(Int32, BASS_WASAPI_DEVICEINFO) can be used to enumerate the available devices.

freq

Type: SystemInt32
The sample rate to use... 0 = "mix format" sample rate.

chans

Type: SystemInt32
The number of channels to use... 0 = "mix format" channels, 1 = mono, 2 = stereo, etc.

flags

Type: Un4seen.BassWasapiBASSWASAPIInit
Any combination of these flags (see BASSWASAPIInit):

BASS_WASAPI_SHARED	Open the device in shared mode.
BASS_WASAPI_EXCLUSIVE	Initialize the device in exclusive mode, else shared mode. The HIWORD - use Utils.MakeLong(flags,format) - can be used to limit the sample format that is used in exclusive mode. The default is to try 32-bit floating-point, 32-bit integer, 24-bit integer, 16-bit integer, 8-bit integer, in that order. A BASS_WASAPI_FORMAT value (see BASS_WASAPI_INFO) can be used to bypass the formats that precede it in that list.
BASS_WASAPI_AUTOFORMAT	Automatically choose another sample format if the specified format is not supported. If possible, a higher sample rate than freq will be used, rather than a lower one.
BASS_WASAPI_BUFFER	Enable double buffering, for use by BASS_WASAPI_GetData(IntPtr, Int32) and BASS_WASAPI_GetLevel. This requires the BASS "no sound" device to have been initilized, via BASS_Init(Int32, Int32, BASSInit, IntPtr, IntPtr).
BASS_WASAPI_EVENT	Enables the event-driven system. Enable event-driven buffering. BASSWASAPI will normally periodically write data to (or read data from) the device's buffer according to the period parameter, but with the event-driven system WASAPI will signal to BASSWASAPI when more data should be written to (or read from) the buffer. So the period parameter is ignored, and buffer is too in shared mode as the system will choose an appropriate buffer length. In exclusive mode, there are 2 buffers of buffer length that are processed alternately. Event-driven buffering is unavailable on loopback devices.
BASS_WASAPI_SAMPLES	buffer and period are in samples rather than seconds.
BASS_WASAPI_DITHER	Requests to apply dither to the output. Dither is optional rather than automatic because it destroys bit-perfect output; you probably don't want to enable it unless you're applying DSP (including volume changes). When the output is floating-point (eg. in shared mode), the flag will have no effect.

buffer

Type: SystemSingle
The length of the device's buffer in seconds. This is a minimum and the driver may choose to use a larger buffer; BASS_WASAPI_GetInfo(BASS_WASAPI_INFO) can be used to confirm what the buffer size is. For an output device, the buffer size determines the latency. With event-driven exclusive mode, there will be 2 buffers of this length, so the total buffer length is double.

period

Type: SystemSingle
The interval (in seconds or samples depending on BASS_WASAPI_SAMPLES) between callback function calls... 0 = use default. If the specified period is below the minimum update period, it will automatically be raised to that. This is ignored when the BASS_WASAPI_EVENT flag is specified, except in shared mode when buffer = 0 on Windows 10 (see remarks).

The update period specifies the time between WASAPIPROC calls. The BASS_WASAPI_DEVICEINFO (see BASS_WASAPI_GetDeviceInfo(Int32, BASS_WASAPI_DEVICEINFO)) "minperiod" and "defperiod" values are actually minimum/default update periods.

proc

Type: Un4seen.BassWasapiWASAPIPROC
The user defined function to process the channel. Use to create a Wasapi "push" device (to which you can feed sample data via BASS_WASAPI_PutData(IntPtr, Int32)).

user

Type: SystemIntPtr
User instance data to pass to the callback function.

Return Value

For convenience, devices are always initialized to use their highest sample resolution and that is then converted to 32-bit floating-point, so that WASAPIPROC callback functions and the BASS_WASAPI_PutData(IntPtr, Int32) and BASS_WASAPI_GetData(IntPtr, Int32) functions are always dealing with the same sample format. The device's sample format can be obtained via BASS_WASAPI_GetInfo(BASS_WASAPI_INFO).

WASAPI does not support arbitrary sample formats, like DirectSound does. In particular, only the "mix format" (available from BASS_WASAPI_GetDeviceInfo(Int32, BASS_WASAPI_DEVICEINFO)) is generally supported in shared mode. BASS_WASAPI_CheckFormat(Int32, Int32, Int32, BASSWASAPIInit) can be used to check whether a particular sample format is supported. The BASSmix add-on can be used to play (or record) in otherwise unsupported sample formats, as well as playing multiple sources.

A loopback device can only be used when the corresponding output device is not being used in exclusive mode, and it will only deliver data when the ouput device does; if the output device produces no data, then the loopback device will capture no data.

Shared mode usually has a fixed period of 10ms, but Windows 10 supports shorter periods, which allows smaller buffers and lower latency. A shorter period (and buffer) can be requested by setting buffer to 0 and period to the length wanted. If the requested period is lower than the device (or Windows) supports, then it will be automatically raised to the minimum supported. It will also be rounded up if it does not match the device's granularity. The actual period in use can be determined from the (minimum) amount of data that gets requested from the WASAPIPROC callback function. The shared mode period is a system-wide setting that affects all users of the device, particular those using event-driven buffering; they will be asked to provide data at the new period. If another process is already using a non-default period, then it will not be possible to set a different period until they finish; the existing period will have to be used in the meantime.

The initialized device will not begin processing data until BASS_WASAPI_Start is called.

Simultaneously using multiple devices is supported in the BASS API via a context switching system; instead of there being an extra "device" parameter in the function calls, the device to be used is set prior to calling the functions. BASS_WASAPI_SetDevice(Int32) is used to switch the current device. When successful, BASS_WASAPI_Init(Int32, Int32, Int32, BASSWASAPIInit, Single, Single, WASAPIPROC, IntPtr) automatically sets the current thread's device to the one that was just initialized.

When using the default output or input device, BASS_WASAPI_GetDevice can be used to find out which device it was mapped to.

In SHARED mode you must initialize the device with the current WASAPI mixer sample rate and number of channels (see the BASS_WASAPI_DEVICEINFO "mixfreq" and "mixchans" properties).

In EXCLUSIVE mode you might use any sample rate and number of channels which are supported by the device/driver.

This function must be successfully called before any input or output can be performed.

In EXCLUSIVE mode, the "period" value will affect what's an acceptable "buffer" value (it appears that the buffer must be at least 4x the period). In SHARED mode, it's the other way round, the "period" will be reduced to fit the "buffer" if necessary (with a minimum of the "defperiod" value). The system will limit them to an acceptable range, so for example, you could use a very small value (eg. 0.0001) for both, to get the minimum possible latency.

Note: When initializing an input (capture or loopback) device, it might be the case, that the device is automatically muted once initialized. You can use the BASS_WASAPI_GetMute(BASSWASAPIVolume)/BASS_WASAPI_SetMute(BASSWASAPIVolume, Boolean) methods to check and probably toggle this.

Reference