Windows Phone 保存录音

　　前面介绍了Windows Phone 录制音频，通过访问Windows Phone的麦克风进行录制音频。录制好的音频要保存为文件，需要做相关格式转换。一般录音的格式为.WAV，下面就介绍如何将录音保存为WAV文件。
　　1.在录制音频开始之前，首先要向音频流存储区audioStream中写入WAV文件头信息。即在调用microphone.Start()之前调用WriteWavHeader(audioStream, microphone.SampleRate)，其中WriteWavHeader函数实现如下。

/// <summary>
/// 写wav文件头信息
/// </summary>
/// <param name="stream"></param>
/// <param name="sampleRate"></param>
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);
}

　　2.在录制音频结束的时候，才能确认录音文件大小的长度，此时需要修改WAV文件头部分信息。即在调用microphone.Stop()之后调用UpdateWavHeader(audioStream)，其中UpdateWavHeader函数实现如下。

/// <summary>
/// 更新wav文件头信息
/// </summary>
/// <param name="stream"></param>
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);
}

　　3.通过以上处理后的audioStream流已经是格式化后的WAV流。接下来只需要将audioStream流写入独立存储中(yu.wav)。

        //将数据流转换为byte，recording中即为音频数据
        byte[] recording = audioStream.ToArray();
        //独立存储文件处理
        using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
        {
            try
            {
                //打开文件
                using (IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream("yu.wav", FileMode.Create, myIsolatedStorage))
                {
                    fileStream.Write(recording, 0, recording.Length);
                }
            }
            catch (Exception ex)
            {
                //读取失败
            }
        }