C# DirectSound - Capture buffers not continuous
- by Wizche
Hi,
I'm trying to capture raw data from my line-in using DirectSound.
My problem is that, from a buffer to another the data are just inconsistent, if for example I capture a sine I see a jump from my last buffer and the new one. To detected this I use a graph widget to draw the first 500 elements of the last buffer and the 500 elements from the new one:
Snapshot
I initialized my buffer this way:
format = new WaveFormat {
SamplesPerSecond = 44100,
BitsPerSample = (short)bitpersample,
Channels = (short)channels,
FormatTag = WaveFormatTag.Pcm
};
format.BlockAlign = (short)(format.Channels * (format.BitsPerSample / 8));
format.AverageBytesPerSecond = format.SamplesPerSecond * format.BlockAlign;
_dwNotifySize = Math.Max(4096, format.AverageBytesPerSecond / 8);
_dwNotifySize -= _dwNotifySize % format.BlockAlign;
_dwCaptureBufferSize = NUM_BUFFERS * _dwNotifySize; // my capture buffer
_dwOutputBufferSize = NUM_BUFFERS * _dwNotifySize / channels; // my output buffer
I set my notifications one at half the buffer and one at the end:
_resetEvent = new AutoResetEvent(false);
_notify = new Notify(_dwCapBuffer);
bpn1 = new BufferPositionNotify();
bpn1.Offset = ((_dwCapBuffer.Caps.BufferBytes) / 2) - 1;
bpn1.EventNotifyHandle = _resetEvent.SafeWaitHandle.DangerousGetHandle();
bpn2 = new BufferPositionNotify();
bpn2.Offset = (_dwCapBuffer.Caps.BufferBytes) - 1;
bpn2.EventNotifyHandle = _resetEvent.SafeWaitHandle.DangerousGetHandle();
_notify.SetNotificationPositions(new BufferPositionNotify[] { bpn1, bpn2 });
observer.updateSamplerStatus("Events listener initialization complete!\r\n");
And here is how I process the events.
/* Process thread */
private void eventReceived()
{
int offset = 0;
_dwCaptureThread = new Thread((ThreadStart)delegate
{
_dwCapBuffer.Start(true);
while (isReady)
{
_resetEvent.WaitOne(); // Notification received
/* Read the captured buffer */
Array read = _dwCapBuffer.Read(offset, typeof(short), LockFlag.None, _dwOutputBufferSize - 1);
observer.updateTextPacket("Buffer: " + count.ToString() + " # " + read.GetValue(read.Length - 1).ToString() + " # " + read.GetValue(0).ToString() + "\r\n");
/* Print last/new part of the buffer to the debug graph */
short[] graphData = new short[1001];
Array.Copy(read, graphData, 1000);
db.SetBufferDebug(graphData, 500);
observer.updateGraph(db.getBufferDebug());
offset = (offset + _dwOutputBufferSize) % _dwCaptureBufferSize;
/* Out buffer not used */
/*_dwDevBuffer.Write(0, read, LockFlag.EntireBuffer);
_dwDevBuffer.SetCurrentPosition(0);
_dwDevBuffer.Play(0, BufferPlayFlags.Default);*/
}
_dwCapBuffer.Stop();
});
_dwCaptureThread.Start();
}
Any advise? I'm sure I'm failing somewhere in the event processing, but I cant find where.
I had developed the same application using the WaveIn API and it worked well.
Thanks a lot...
