BASS.NET API for the Un4seen BASS Audio LibraryBassEncBASS_Encode_StartACM Method (Int32, ACMFORMAT, BASSEncode, ENCODEPROC, IntPtr)BASS.NET API for the Un4seen BASS Audio Library
Sets up an encoder on a channel, using an ACM codec and sending the output to a user defined function.

Namespace: Un4seen.Bass.AddOn.Enc
Assembly: Bass.Net (in Bass.Net.dll) Version: 2.4.12.0
Syntax

[DllImportAttribute("bassenc.dll", CharSet = CharSet.Auto)]
public static int BASS_Encode_StartACM(
	int handle,
	ACMFORMAT form,
	BASSEncode flags,
	ENCODEPROC proc,
	IntPtr user
)

Parameters

handle
Type: SystemInt32
The channel handle... a HSTREAM, HMUSIC, or HRECORD.
form
Type: Un4seen.Bass.AddOn.EncACMFORMAT
ACM codec output format (an ACMFORMAT instance as returned by BASS_Encode_GetACMFormat(Int32, IntPtr, Int32, String, BASSACMFormat)).
flags
Type: Un4seen.Bass.AddOn.EncBASSEncode
A combination of these flags BASSEncode:
BASS_ENCODE_PAUSEStart the encoder paused.
BASS_ENCODE_AUTOFREEAutomatically free the encoder when the source channel is freed.
BASS_ENCODE_QUEUEQueue data to feed the encoder asynchronously. This prevents the data source (DSP system or BASS_Encode_Write(Int32, IntPtr, Int32) call) getting blocked by the encoder, but if data is queud more quickly than the encoder can process it, that could result in lost data.
BASS_ENCODE_CAST_NOLIMITDon't limit the data rate (to real-time speed) when sending to a Shoutcast or Icecast server.
BASS_ENCODE_LIMITLimit the data rate to real-time speed, by introducing a delay when the rate is too high. With BASS 2.4.6 or above, this flag is ignored when the encoder is fed in a playback buffer update cycle (including BASS_Update(Int32) and BASS_ChannelUpdate(Int32, Int32) calls), to avoid possibly causing playback buffer underruns. Except for in those instances, this flag is applied automatically when the encoder is feeding a Shoutcast or Icecast server.
proc
Type: Un4seen.Bass.AddOn.EncENCODEPROC
Callback function to receive the encoded data.
user
Type: SystemIntPtr
User instance data to pass to the callback function.

Return Value

Type: Int32
The encoder handle is returned if the encoder is successfully started, else 0 is returned. Use BASS_ErrorGetCode to get the error code.
Remarks

The ACM encoder allows installed ACM (Audio Compression Manager) codecs to be used for encoding. The codec used is determined by the contents of the form parameter. The BASS_Encode_GetACMFormat(Int32, IntPtr, Int32, String, BASSACMFormat) function can be used to initialize that.

Internally, the sending of sample data to the encoder is implemented via a DSP callback on the channel. That means when you play the channel (or call BASS_ChannelGetData(Int32, IntPtr, Int32) if it's a decoding channel), the sample data will be sent to the encoder at the same time. The encoding is performed in the DSP callback. There isn't a separate process doing the encoding, as when using an external encoder via BASS_Encode_Start(Int32, String, BASSEncode, ENCODEPROC, IntPtr).

By default, the encoder DSP has a priority setting of -1000, which determines where in the DSP chain the encoding is performed. That can be changed using the BASS_CONFIG_ENCODE_PRIORITY config option (see BASS_SetConfig(BASSConfig, Int32)).

Besides the automatic DSP system, data can also be manually fed to the encoder via the BASS_Encode_Write(Int32, IntPtr, Int32) function. Both methods can be used together, but in general, the "automatic" system ought be paused when using the "manual" system, by use of the BASS_ENCODE_PAUSE flag or the BASS_Encode_SetPaused(Int32, Boolean) function.

When queued encoding is enabled via the BASS_ENCODE_QUEUE flag, the DSP system or BASS_Encode_Write(Int32, IntPtr, Int32) call will just buffer the data, and the data will then be fed to the encoder by another thread. The buffer will grow as needed to hold the queued data, up to a limit specified by the BASS_CONFIG_ENCODE_QUEUE config option. If the limit is exceeded (or there is no free memory), data will be lost; BASS_Encode_SetNotify(Int32, ENCODENOTIFYPROC, IntPtr) can be used to be notified of that occurrence. The amount of data that is currently queued, as well as the queue limit and how much data has been lost, is available from BASS_Encode_GetCount(Int32, BASSEncodeCount).

When done encoding, use BASS_Encode_Stop(Int32) to close the encoder.

Multiple encoders can be set on a channel. For simplicity, the encoder functions will accept either an encoder handle or a channel handle. When using a channel handle, the function is applied to all encoders that are set on that channel.

ERROR CODEDescription
BASS_ERROR_HANDLEhandle is not valid.
BASS_ERROR_NOTAVAILThe codec specified in form couldn't be initialized.
BASS_ERROR_UNKNOWNSome other mystery problem!

Examples

Setup an ACM encoder with a callback to process the encoded data:
VB
Private _myEncProc As ENCODEPROC
Private _encbuffer As Byte() = Nothing
...
Dim codec As ACMFORMAT = BassEnc.BASS_Encode_GetACMFormat(channel, "Select your encoder", 
                                 BASSACMFormat.BASS_ACM_DEFAULT, WAVEFormatTag.UNKNOWN)
If Not (codec Is Nothing) Then
  ' create the delegate
  _myEncProc = New ENCODEPROC(AddressOf MyEncoderProc)
  ' begin encoding using the codec with the delegate callback
  Dim encHandle As Integer = BassEnc.BASS_Encode_StartACM(channel, codec, 
                                     BASSEncode.BASS_ENCODE_DEFAULT, _myEncProc, IntPtr.Zero)
End If
...
Private Function MyEncodingWriter(handle As Integer, channel As Integer, 
                                  buffer As IntPtr, length As Integer, user As IntPtr) As Boolean
  ' dynamic buffer allocation
  If _encbuffer Is Nothing OrElse _encbuffer.Length < length Then
    _encbuffer = New Byte(length) {}
  End If 

  ' copy from managed to unmanaged memory
  Marshal.Copy(buffer, _encbuffer, 0, length)
  ' process the data in _encbuffer, e.g. write to disk or whatever
  ...
End Function
// the encoding callback
private ENCODEPROC _myEncProc;
private byte[] _encbuffer = null;
...
ACMFORMAT codec = BassEnc.BASS_Encode_GetACMFormat(channel, "Select your encoder", 
                          BASSACMFormat.BASS_ACM_DEFAULT, WAVEFormatTag.UNKNOWN);
if ( codec != null )
{
  // create the delegate
  _myEncProc = new ENCODEPROC(MyEncoderProc);
  // begin encoding using the codec with the delegate callback
  int encHandle = BassEnc.BASS_Encode_StartACM( channel, codec, 
                          BASSEncode.BASS_ENCODE_DEFAULT, _myEncProc, IntPtr.Zero);
}
...
private bool MyEncodingWriter(int handle, int channel, IntPtr buffer, int length, IntPtr user)
{
  // dynamic buffer allocation
  if ( _encbuffer == null || _encbuffer.Length < length )
    _encbuffer = new byte[length];

  // copy from managed to unmanaged memory
  Marshal.Copy(buffer, _encbuffer, 0, length);
  // process the data in _encbuffer, e.g. write to disk or whatever
  ...
}
If you are into C# you might also use native pointer access in an unsafe codeblock:
private unsafe void MyEncoding(int handle, int channel, IntPtr buffer, int length, IntPtr user)
{
  // here we receive the encoded data back.
  // the encoded data is a kind of raw byte buffer...
  byte *data = (byte*)buffer;

  for (int a=0; a<length; a++)
  {
    // do whatever you want with the encoded data
    _stream.WriteByte( data[a] );
  }
}
See Also

Reference