BassBASS_RecordStart Method (Int32, Int32, BASSFlag, Int32, RECORDPROC, IntPtr)

public static int BASS_RecordStart(
	int freq,
	int chans,
	BASSFlag flags,
	int period,
	RECORDPROC proc,
	IntPtr user
)

Public Shared Function BASS_RecordStart ( 
	freq As Integer,
	chans As Integer,
	flags As BASSFlag,
	period As Integer,
	proc As RECORDPROC,
	user As IntPtr
) As Integer

Parameters

freq

Type: SystemInt32
The sample rate to record at.

chans

Type: SystemInt32
The number of channels... 1 = mono, 2 = stereo.

flags

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

BASS_SAMPLE_8BITS	Use 8-bit resolution. If neither this or the BASS_SAMPLE_FLOAT flags are specified, then the recorded data is 16-bit.
BASS_SAMPLE_FLOAT	Use 32-bit floating-point sample data. WDM drivers are required to use this flag in Windows. See Floating-point channels for more information.
BASS_RECORD_PAUSE	Start the recording paused. Use BASS_ChannelPlay(Int32, Boolean) together with the handle returned by this method to start it.

period

Type: SystemInt32
Set the period (in milliseconds) between calls to the callback function (RECORDPROC). The minimum period is 5ms, the maximum the maximum is half the BASS_CONFIG_REC_BUFFER setting. If the period specified is outside this range, it is automatically capped. The default is 100ms.

proc

Type: Un4seen.BassRECORDPROC
The user defined function to receive the recorded sample data... can be if you do not wish to use a callback.

user

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

Return Value

The sample data will generally arrive from the recording device in blocks rather than in a continuous stream, so when specifying a very short period between callbacks, some calls may be skipped due to there being no new data available since the last call.

When specifying a very short period between RECORDPROC calls, some calls may be skipped due to there being no new data available from the recording device since the last call. This is more likely to happen with drivers that do not have hardware support.

Starting the recording paused (BASS_RECORD_PAUSE) allows DSP/FX to be set on the recording channel before any data reaches the RECORDPROC function.

Not using a callback (proc = ) allows lower latency for full-duplex recording (ie. playing the data as it's being recorded), as you get the recorded data on demand via the BASS_ChannelGetData(Int32, IntPtr, Int32) function. To keep latency at a minimum, the amount of data in the recording buffer should be monitored (also done via BASS_ChannelGetData(Int32, IntPtr, Int32), with the BASS_DATA_AVAILABLE flag) to check that there's not too much data; freshly recorded data will only be retrieved after the older data in the buffer is.

When freq and/or chans is set to 0 for the device's current values, BASS_ChannelGetInfo(Int32, BASS_CHANNELINFO) can be used afterwards to find out what values are being used by the recording.

A recording may end unexpectedly if the device fails, eg. if it is disconnected/disabled. A BASS_SYNC_DEV_FAIL sync can be set via BASS_ChannelSetSync(Int32, BASSSync, Int64, SYNCPROC, IntPtr) to be informed if that happens. It will not be possible to resume the recording channel then; a new recording channel will need to be created when the device becomes available again.

Platform-specific

Multiple simultaneous recordings can be made from the same device on Windows XP and later, but generally not on older Windows. Multiple simultaneous recordings are possible on macOS and iOS, but may not always be on Linux. Loopback recording is only available on Windows Vista and above. The option to use the device's current sample rate and/or channel count is only available on Windows/macOS/iOS. On macOS and iOS, the device is instructed (when possible) to deliver data at the period set in the HIWORD of flags, even when a callback function is not used. On other platforms, it is up the the system when data arrives from the device. On macOS and iOS, this function may succeed but only capture silence when recording permission has not been granted. The AVCaptureDevice authorizationStatusForMediaType method (or the AVAudioSession recordPermission method on iOS) can be used to check the permission status.

private RECORDPROC _myRecProc; // make it global, so that the Garbage Collector can not remove it
...
Bass.BASS_RecordInit(-1);
_myRecProc = new RECORDPROC(MyRecording);
// start recording paused
int recChannel = Bass.BASS_RecordStart(44100, 2, BASSFlag.BASS_RECORD_PAUSE, 50, _myRecProc, IntPtr.Zero);
...
// really start recording
Bass.BASS_ChannelPlay(recChannel, false);
...
// the recording callback
private bool MyRecording(int handle, IntPtr buffer, int length, IntPtr user)
{
  return true;
}

Private _myRecProc As RECORDPROC
...
Bass.BASS_RecordInit(-1)
_myRecProc = New RECORDPROC(AddressOf MyRecording)
' start recording paused
Dim recChannel As Integer = Bass.BASS_RecordStart(44100, 2, BASSFlag.BASS_RECORD_PAUSE, 50, _myRecProc, IntPtr.Zero)
...
' really start recording
Bass.BASS_ChannelPlay(recChannel, False)
...
' the recording callback
Private Function MyRecording(handle As Integer, buffer As IntPtr, length As Integer, user As IntPtr) As Boolean
  Return True
End Function

Reference