How to read the data in a wav file to an array

NOTE: As per Daniel Moller's comment, refer to http://soundfile.sapp.org/doc/WaveFormat/ to understand the code. (And upvote the comment).

At time of writing nobody has addressed 32-bit or 64-bit encoded WAVs.

The following code handles 16/32/64 bit and mono/stereo:

static bool readWav( string filename, out float[] L, out float[] R )
{
    L = R = null;

    try {
        using (FileStream fs = File.Open(filename,FileMode.Open))
        {
            BinaryReader reader = new BinaryReader(fs);

            // chunk 0
            int chunkID       = reader.ReadInt32();
            int fileSize      = reader.ReadInt32();
            int riffType      = reader.ReadInt32();
            

            // chunk 1
            int fmtID         = reader.ReadInt32();
            int fmtSize       = reader.ReadInt32(); // bytes for this chunk (expect 16 or 18)

            // 16 bytes coming...
            int fmtCode       = reader.ReadInt16();
            int channels      = reader.ReadInt16();
            int sampleRate    = reader.ReadInt32();
            int byteRate      = reader.ReadInt32();
            int fmtBlockAlign = reader.ReadInt16();
            int bitDepth      = reader.ReadInt16();

            if (fmtSize == 18)
            {
                // Read any extra values
                int fmtExtraSize = reader.ReadInt16();
                reader.ReadBytes(fmtExtraSize);
            }

            // chunk 2
            int dataID = reader.ReadInt32();
            int bytes = reader.ReadInt32();
            
            // DATA!
            byte[] byteArray = reader.ReadBytes(bytes);
            
            int bytesForSamp = bitDepth/8;
            int nValues = bytes / bytesForSamp;


            float[] asFloat = null;
            switch( bitDepth ) {
                case 64:
                    double[] 
                        asDouble = new double[nValues];  
                    Buffer.BlockCopy(byteArray, 0, asDouble, 0, bytes);
                    asFloat = Array.ConvertAll( asDouble, e => (float)e );
                    break;
                case 32:
                    asFloat = new float[nValues];   
                    Buffer.BlockCopy(byteArray, 0, asFloat, 0, bytes);
                    break;
                case 16:
                    Int16 [] 
                        asInt16 = new Int16[nValues];   
                    Buffer.BlockCopy(byteArray, 0, asInt16, 0, bytes);
                    asFloat = Array.ConvertAll( asInt16, e => e / (float)(Int16.MaxValue+1) );
                    break;
                default:
                    return false;
            }

            switch( channels ) {
            case 1:
                L = asFloat;
                R = null;
                return true;
            case 2:
                // de-interleave
                int nSamps = nValues / 2;
                L = new float[nSamps];
                R = new float[nSamps];
                for( int s=0, v=0; s<nSamps; s++ ) {
                    L[s] = asFloat[v++];
                    R[s] = asFloat[v++];
                }
                return true;
            default:
                return false;
            }
        }
    }
    catch {
            Debug.Log( "...Failed to load: " + filename );
            return false;
    }

    return false;
}

This code should do the trick. It converts a wave file to a normalized double array (-1 to 1), but it should be trivial to make it an int/short array instead (remove the /32768.0 bit and add 32768 instead). The right[] array will be set to null if the loaded wav file is found to be mono.

I can't claim it's completely bullet proof (potential off-by-one errors), but after creating a 65536 sample array, and creating a wave from -1 to 1, none of the samples appear to go 'through' the ceiling or floor.

// convert two bytes to one double in the range -1 to 1
static double bytesToDouble(byte firstByte, byte secondByte) {
    // convert two bytes to one short (little endian)
    short s = (secondByte << 8) | firstByte;
    // convert to range from -1 to (just below) 1
    return s / 32768.0;
}

// Returns left and right double arrays. 'right' will be null if sound is mono.
public void openWav(string filename, out double[] left, out double[] right)
{
    byte[] wav = File.ReadAllBytes(filename);

    // Determine if mono or stereo
    int channels = wav[22];     // Forget byte 23 as 99.999% of WAVs are 1 or 2 channels

    // Get past all the other sub chunks to get to the data subchunk:
    int pos = 12;   // First Subchunk ID from 12 to 16

    // Keep iterating until we find the data chunk (i.e. 64 61 74 61 ...... (i.e. 100 97 116 97 in decimal))
    while(!(wav[pos]==100 && wav[pos+1]==97 && wav[pos+2]==116 && wav[pos+3]==97)) {
        pos += 4;
        int chunkSize = wav[pos] + wav[pos + 1] * 256 + wav[pos + 2] * 65536 + wav[pos + 3] * 16777216;
        pos += 4 + chunkSize;
    }
    pos += 8;

    // Pos is now positioned to start of actual sound data.
    int samples = (wav.Length - pos)/2;     // 2 bytes per sample (16 bit sound mono)
    if (channels == 2) samples /= 2;        // 4 bytes per sample (16 bit stereo)

    // Allocate memory (right will be null if only mono sound)
    left = new double[samples];
    if (channels == 2) right = new double[samples];
    else right = null;

    // Write to double array/s:
    int i=0;
    while (pos < length) {
        left[i] = bytesToDouble(wav[pos], wav[pos + 1]);
        pos += 2;
        if (channels == 2) {
            right[i] = bytesToDouble(wav[pos], wav[pos + 1]);
            pos += 2;
        }
        i++;
    }
}

Assuming your WAV file contains 16 bit PCM (which is the most common), you can use NAudio to read it out into a byte array, and then copy that into an array of 16 bit integers for convenience. If it is stereo, the samples will be interleaved left, right.

using (WaveFileReader reader = new WaveFileReader("myfile.wav"))
{
    Assert.AreEqual(16, reader.WaveFormat.BitsPerSample, "Only works with 16 bit audio");
    byte[] buffer = new byte[reader.Length];
    int read = reader.Read(buffer, 0, buffer.Length);
    short[] sampleBuffer = new short[read / 2];
    Buffer.BlockCopy(buffer, 0, sampleBuffer, 0, read);
}

I know you wanted to avoid third party libraries, but if you want to be sure to cope with WAV files with extra chunks, I suggest avoiding approaches like just seeking 44 bytes into the file.