Table of Contents

This article explains how to get audio input from the microphone, convert it to .wav format, and save it to IsolatedStorage.

 

Introduction

As the microphone's stream buffer provide raw data we need to convert it into a well known file format before saving in order to allow users to play the recorded file everywhere. The easiest solution is to use the .wav fileformat.

Microphone Sample demonstrates how to get audio input from the microphone in aSilverlight for Windows Phone application. This project is used in this guide and we will be focused on saving process.

 

Note
This article was created using un-attributed code samples from the Internet. Dmehers asserts theorigin of this information is his blog post: Storing WP7 recordedaudio as WAV format streams.

 

Saving into WAV format

As we use isolated storage we need to use the following namespaces:

using System.Windows;
using System.IO.IsolatedStorage;
using System.Windows.Resources;

 

Then add the following functions to your code:

private void SaveToIsolatedStorage()
{
 // first, we grab the current apps isolated storage handle
 IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
  
 // we give our file a filename
 string strSaveName = "myFile.wav";
  
 // if that file exists...
 if (isf.FileExists(strSaveName))
 {
 // then delete it
 isf.DeleteFile(strSaveName);
 }
  
 // now we set up an isolated storage stream to point to store our data
 IsolatedStorageFileStream isfStream =
 new IsolatedStorageFileStream(strSaveName,
 FileMode.Create, IsolatedStorageFile.GetUserStoreForApplication());
  
 isfStream.Write(stream.ToArray(), 0, stream.ToArray().Length);
  
 // ok, done with isolated storage... so close it
 isfStream.Close();
}
  
public void UpdateWavHeader(Stream stream)
{
 if (!stream.CanSeek) throw new Exception("Can't seek stream to update wav header");
  
 var oldPos = stream.Position;
  
 // ChunkSize 36 + SubChunk2Size
 stream.Seek(4, SeekOrigin.Begin);
 stream.Write(BitConverter.GetBytes((int)stream.Length - 8), 0, 4);
  
 // Subchunk2Size == NumSamples * NumChannels * BitsPerSample/8 This is the number of bytes in the data.
 stream.Seek(40, SeekOrigin.Begin);
 stream.Write(BitConverter.GetBytes((int)stream.Length - 44), 0, 4);
  
 stream.Seek(oldPos, SeekOrigin.Begin);
}
  
 public void WriteWavHeader(Stream stream, int sampleRate)
{
 const int bitsPerSample = 16;
 const int bytesPerSample = bitsPerSample / 8;
 var encoding = System.Text.Encoding.UTF8;
  
 // ChunkID Contains the letters "RIFF" in ASCII form (0x52494646 big-endian form).
 stream.Write(encoding.GetBytes("RIFF"), 0, 4);
  
 // NOTE this will be filled in later
 stream.Write(BitConverter.GetBytes(0), 0, 4);
  
 // Format Contains the letters "WAVE"(0x57415645 big-endian form).
 stream.Write(encoding.GetBytes("WAVE"), 0, 4);
  
 // Subchunk1ID Contains the letters "fmt " (0x666d7420 big-endian form).
 stream.Write(encoding.GetBytes("fmt "), 0, 4);
  
 // Subchunk1Size 16 for PCM. This is the size of therest of the Subchunk which follows this number.
 stream.Write(BitConverter.GetBytes(16), 0, 4);
  
 // AudioFormat PCM = 1 (i.e. Linear quantization) Values other than 1 indicate some form of compression.
 stream.Write(BitConverter.GetBytes((short)1), 0, 2);
  
 // NumChannels Mono = 1, Stereo = 2, etc.
 stream.Write(BitConverter.GetBytes((short)1), 0, 2);
  
 // SampleRate 8000, 44100, etc.
 stream.Write(BitConverter.GetBytes(sampleRate), 0, 4);
  
 // ByteRate = SampleRate * NumChannels * BitsPerSample/8
 stream.Write(BitConverter.GetBytes(sampleRate * bytesPerSample), 0, 4);
  
 // BlockAlign NumChannels * BitsPerSample/8 The number of bytes for one sample including all channels.
 stream.Write(BitConverter.GetBytes((short)(bytesPerSample)), 0, 2);
  
 // BitsPerSample 8 bits = 8, 16 bits = 16, etc.
 stream.Write(BitConverter.GetBytes((short)(bitsPerSample)), 0, 2);
  
 // Subchunk2ID Contains the letters "data" (0x64617461 big-endian form).
 stream.Write(encoding.GetBytes("data"), 0, 4);
  
 // NOTE to be filled in later
 stream.Write(BitConverter.GetBytes(0), 0, 4);
}

On function delegated to begin the record process include the call to WriteWavHeader() before the microphone.Start() function

private void recordButton_Click(object sender, EventArgs e)
 
{
...
stream.SetLength(0);
 
WriteWavHeader(stream, microphone.SampleRate);
 
// Start recording
microphone.Start();
...
}

After microphone.Stop() add the call to UpdateWavHeader and to SaveToIsolatedStorage

microphone.Stop();
UpdateWavHeader(stream);
SaveToIsolatedStorage();

Related links

 

Credits

Originally contributed on 3 September 2012? by galazzo