Naudio ImaAdpcmWaveFormat, BufferedWaveprovider not happy

I am working on an application where I use Naudio to play sound streamed to/from a modem (no luck with tapi on this particular modem, so AT-commands).

This works acceptably well when I used a linear waveformat (WaveFormat waveFormat = new WaveFormat(8000, 16, 1);) but now I want to try getting full duplex, which means that using a slightly more efficient sound format is probably a good idea.

Saw that Naudio has an ImaAdpcmWaveFormat, so tried to replace the WaveFormat object with that one (ImaAdpcmWaveFormat imaadpcm_waveformat = new ImaAdpcmWaveFormat(8000, 1, 4);).

However, now the waveout.init throws a System.DivideByZeroException :(.

I had a similar problem when I had managed to misread the specification for WaveFormat and put 2 instead of 16 for "bits", but 4 bits/sample should be an acceptable rate for IMA ADPCM? Anyhow, same exception for 8 or 16 bits/sample...

Exception data:

System.DivideByZeroException HResult=0x80020012 Message=Attempted to divide by zer0. Source=NAudio StackTrace:
at NAudio.Wave.WaveFormat.ConvertLatencyToByteSize(Int32 milliseconds)
at NAudio.Wave.WaveOut.Init(IWaveProvider waveProvider)
at USRModemTest.Form1..ctor() in C:\Users\c\Source\Repos\USRModemTest\USRModemTest\Form1.cs:line 56
at USRModemTest.Program.Main() in C:\Users\c\Source\Repos\USRModemTest\USRModemTest\Program.cs:line 19

From the constructor:

Note that this works acceptably well if I replace imaadpcm_waveformat with waveFormat

//waveFormat = new WaveFormat(8000, 16, 1);
imaadpcm_waveformat = new ImaAdpcmWaveFormat(8000, 1, 4);

//bwp_ModemToSpeakers = new BufferedWaveProvider(waveFormat);
bwp_ModemToSpeakers = new BufferedWaveProvider(imaadpcm_waveformat);
bwp_ModemToSpeakers.DiscardOnBufferOverflow = true;
//bwp_ModemToSpeakers.BufferDuration = System.TimeSpan.FromMilliseconds(200);
bwp_ModemToSpeakers.ReadFully = true;
bwp_ModemToSpeakers.BufferLength = 1000 ; // as small as possible it seems

waveout = new WaveOut();
waveout.DeviceNumber = -1; // default communications device
waveout.DesiredLatency = 200;
waveout.Init(bwp_ModemToSpeakers);

You cannot play audio encoded with IMA ADPCM directly. I recommend you decode the audio into PCM before placing it into BufferedWaveProvider. Examples of this can be found in the NAudio demo project and you can make use of the AcmStream class for the conversion.