C# - WAV 기본 파일 포맷

wav 파일은 그 포맷이 무척 간단합니다. (사실, 간단하게 다룰 수 있는 경우가 대다수일 뿐입니다. ^^;)

What is a WAV file? 
; https://docs.fileformat.com/audio/wav/

4.웨이브 파일의 구조
; http://www.soen.kr/lecture/library/waveform/4.htm

using System.Runtime.InteropServices;
using System.Text;

namespace Wave;

public class WaveFile
{
    string _filePath = "";
    WaveHeader _header;
    public WaveHeader Header => _header;

    private WaveFile() { }

    public WaveFile(string path)
    {
        _filePath = path;
        _header = GetHeader();
    }

    public WaveHeader GetHeader()
    {
        byte[] buffer = new byte[Marshal.SizeOf<WaveHeader>()];
        using (FileStream fs = File.OpenRead(_filePath))
        {
            fs.Read(buffer);
        }

        return structFromBytes(buffer);
    }

    private WaveHeader structFromBytes(byte[] buffer)
    {
        GCHandle pData = GCHandle.Alloc(buffer, GCHandleType.Pinned);
        WaveHeader instance = Marshal.PtrToStructure<WaveHeader>(pData.AddrOfPinnedObject());
        pData.Free();

        return instance;
    }
}

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi)]
public struct WaveHeader
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string ChunkId;

    public int FileSize; /* Size of the file - 8 bytes */

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string TypeHeader;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string FormatMarker;

    public int SubChunkSize; /* 16, ChunkId부터 FormatMarker 필드까지의 크기 */

    public short AudioFormat; /* 1 is PCM */

    public short Channels;

    public int SampleRate;

    public int ByteRate; /* (Sample Rate * BitsPerSample * Channels) / 8 */

    public short BlockAlign; /* (BitsPerSample * Channels) / 8.1 - 8 bit mono2 - 8 bit stereo/16 bit mono4 - 16 bit stereo */

    public short BitsPerSample;

    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string DataChunkHeader;

    public int DataSize; /* Size of the data section: SizeOf(wave_file) - Header(44) */
    
    public override string ToString()
    {
        return $"ChunkId: {ChunkId}, FileSize: {FileSize}, TypeHeader: {TypeHeader}, FormatMarker: {FormatMarker
            }, SubChunkSize: {SubChunkSize}, AudioFormat: {AudioFormat}, Channels: {Channels}, SampleRate: {SampleRate
            }, ByteRate: {ByteRate}, BlockAlign: {BlockAlign}, BitsPerSample: {BitsPerSample}, DataChunkHeader: {DataChunkHeader
            }, DataSize: {DataSize}";
    }
}

using Wave;

namespace ConsoleApp1;

internal class Program
{
    static void Main(string[] args)
    {
        string waveFilePath = @"C:\Windows\Media\Alarm01.wav";
        WaveFile wf = new WaveFile(waveFilePath);

        Console.WriteLine(wf.Header);
    }
}

public class WaveFile
{
    // ...[생략]...

    internal static void Create(string filePath, int sampleRate, short bitsPerSample, short channels, byte[] data)
    {
        int headerSize = Marshal.SizeOf<WaveHeader>();

        using (FileStream fs = File.Create(filePath))
        using (BinaryWriter bw = new BinaryWriter(fs, Encoding.ASCII))
        {
            bw.Write(Encoding.ASCII.GetBytes("RIFF"), 0, 4);
            bw.Write(headerSize + data.Length - 8);
            bw.Write(Encoding.ASCII.GetBytes("WAVE"), 0, 4);
            bw.Write(Encoding.ASCII.GetBytes("fmt "), 0, 4);
            bw.Write(16);
            bw.Write((short)1); // 1 is PCM
            bw.Write(channels);
            bw.Write(sampleRate);
            bw.Write((sampleRate * bitsPerSample * channels) / 8); // ByteRate
            bw.Write((short)((bitsPerSample * channels) / 8)); // BlockAlign
            
            bw.Write(bitsPerSample);
            bw.Write(Encoding.ASCII.GetBytes("data"), 0, 4);
            bw.Write(data.Length);

            fs.Write(data);
        }
    }
}