Create valid wav file header for streams in memory

Question

I have raw-headerless wav audio data as MemoryStreams.

Stream rawAudioStream = Producer.GetRawAudioFileStream(...);

I know those streams data format:

// WaveFormat(int rate, int bits, int channels);
WaveFormat waveformat = new WaveFormat(8000, 16, 1);

What I want is to add programmatically right header info for those memory streams without writing them to a physical file.

How can I do that?

PS: I checked the NAudio Library but only found a way to create a header by writing streams to really-physical files which is not suitable for my situation.

var waveformat = new WaveFormat(8000,16,1);

var reader = new RawSourceWaveStream(rawAudioMemStream, waveformat);

using (var convertedStream = WaveFormatConversionStream.CreatePcmStream(reader))    
{
    WaveFileWriter.CreateWaveFile(fileName, convertedStream);     
}

rawAudioMemStream.Close();

Emboss

CreateWaveFile() is just a convenience method. You can also create a WaveFileWriter with the new operator, it has a constructor that takes a Stream. You can pass a MemoryStream. Not that it makes any difference, it is just as fast. – Unbeatable

Answer 1

The below code will write a Wav header to the beginning of a MemoryStream. Which means you'll need to write the header to your stream first, and then you can write your samples. Otherwise the samples at the start of your stream will get overwritten with meta data,

// totalSampleCount needs to be the combined count of samples of all channels. So if the left and right channels contain 1000 samples each, then totalSampleCount should be 2000.
// isFloatingPoint should only be true if the audio data is in 32-bit floating-point format.

private void WriteWavHeader(MemoryStream stream, bool isFloatingPoint, ushort channelCount, ushort bitDepth, int sampleRate, int totalSampleCount)
{
    stream.Position = 0;

    // RIFF header.
    // Chunk ID.
    stream.Write(Encoding.ASCII.GetBytes("RIFF"), 0, 4);

    // Chunk size.
    stream.Write(BitConverter.GetBytes(((bitDepth / 8) * totalSampleCount) + 36), 0, 4);

    // Format.
    stream.Write(Encoding.ASCII.GetBytes("WAVE"), 0, 4);



    // Sub-chunk 1.
    // Sub-chunk 1 ID.
    stream.Write(Encoding.ASCII.GetBytes("fmt "), 0, 4);

    // Sub-chunk 1 size.
    stream.Write(BitConverter.GetBytes(16), 0, 4);

    // Audio format (floating point (3) or PCM (1)). Any other format indicates compression.
    stream.Write(BitConverter.GetBytes((ushort)(isFloatingPoint ? 3 : 1)), 0, 2);

    // Channels.
    stream.Write(BitConverter.GetBytes(channelCount), 0, 2);

    // Sample rate.
    stream.Write(BitConverter.GetBytes(sampleRate), 0, 4);

    // Bytes rate.
    stream.Write(BitConverter.GetBytes(sampleRate * channelCount * (bitDepth / 8)), 0, 4);

    // Block align.
    stream.Write(BitConverter.GetBytes((ushort)channelCount * (bitDepth / 8)), 0, 2);

    // Bits per sample.
    stream.Write(BitConverter.GetBytes(bitDepth), 0, 2);



    // Sub-chunk 2.
    // Sub-chunk 2 ID.
    stream.Write(Encoding.ASCII.GetBytes("data"), 0, 4);

    // Sub-chunk 2 size.
    stream.Write(BitConverter.GetBytes((bitDepth / 8) * totalSampleCount), 0, 4);
}

Maurice

How can I get totalSampleCount from stream? It's something I can get from length? – Marital

Answer 2

It's easy to create custom class to marshal raw data:

    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    public class WavePcmFormat
    {
        /* ChunkID          Contains the letters "RIFF" in ASCII form */
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        private char[] chunkID = new char[] { 'R', 'I', 'F', 'F' };

        /* ChunkSize        36 + SubChunk2Size */
        [MarshalAs(UnmanagedType.U4, SizeConst = 4)]
        private uint chunkSize = 0;

        /* Format           The "WAVE" format name */
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        private char[] format = new char[] { 'W', 'A', 'V', 'E' };

        /* Subchunk1ID      Contains the letters "fmt " */
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        private char[] subchunk1ID = new char[] { 'f', 'm', 't', ' ' };

        /* Subchunk1Size    16 for PCM */
        [MarshalAs(UnmanagedType.U4, SizeConst = 4)]
        private uint subchunk1Size = 16;

        /* AudioFormat      PCM = 1 (i.e. Linear quantization) */
        [MarshalAs(UnmanagedType.U2, SizeConst = 2)]
        private ushort audioFormat = 1;

        /* NumChannels      Mono = 1, Stereo = 2, etc. */
        [MarshalAs(UnmanagedType.U2, SizeConst = 2)]
        private ushort numChannels = 1;
        public ushort NumChannels { get => numChannels; set => numChannels = value; }

        /* SampleRate       8000, 44100, etc. */
        [MarshalAs(UnmanagedType.U4, SizeConst = 4)]
        private uint sampleRate = 44100;
        public uint SampleRate { get => sampleRate; set => sampleRate = value; }

        /* ByteRate         == SampleRate * NumChannels * BitsPerSample/8 */
        [MarshalAs(UnmanagedType.U4, SizeConst = 4)]
        private uint byteRate = 0;

        /* BlockAlign       == NumChannels * BitsPerSample/8 */
        [MarshalAs(UnmanagedType.U2, SizeConst = 2)]
        private ushort blockAlign = 0;

        /* BitsPerSample    8 bits = 8, 16 bits = 16, etc. */
        [MarshalAs(UnmanagedType.U2, SizeConst = 2)]
        private ushort bitsPerSample = 16;
        public ushort BitsPerSample { get => bitsPerSample; set => bitsPerSample = value; }
                
        /* Subchunk2ID      Contains the letters "data" */
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        private char[] subchunk2ID = new char[] { 'd', 'a', 't', 'a' };

        /* Subchunk2Size    == NumSamples * NumChannels * BitsPerSample/8 */
        [MarshalAs(UnmanagedType.U4, SizeConst = 4)]
        private uint subchunk2Size = 0;

        /* Data             The actual sound data. */
        public byte[] Data { get; set; } = new byte[0];

        public WavePcmFormat(byte[] data, ushort numChannels = 2, uint sampleRate = 44100, ushort bitsPerSample = 16)
        {
            Data = data;
            NumChannels = numChannels;
            SampleRate = sampleRate;
            BitsPerSample = bitsPerSample;
        }

        private void CalculateSizes()
        {
            subchunk2Size = (uint)Data.Length;
            blockAlign = (ushort)(NumChannels * BitsPerSample / 8);
            byteRate = SampleRate * NumChannels * BitsPerSample / 8;
            chunkSize = 36 + subchunk2Size;
        }

        public byte[] ToBytesArray()
        {
            CalculateSizes();
            int headerSize = Marshal.SizeOf(this);
            IntPtr headerPtr = Marshal.AllocHGlobal(headerSize);
            Marshal.StructureToPtr(this, headerPtr, false);
            byte[] rawData = new byte[headerSize + Data.Length];
            Marshal.Copy(headerPtr, rawData, 0, headerSize);
            Marshal.FreeHGlobal(headerPtr);
            Array.Copy(Data, 0, rawData, 44, Data.Length);
            return rawData;
        }
    }

Usage:

var wav = new WavePcmFormat(rawDataWithoutHeader, numChannels: 1, sampleRate: SampleRateHertz, bitsPerSample: 16);
var rawDataWithHeader = wav.ToBytesArray();

Sartre