AudioDecoder.cs

using NAudio.Vorbis;
using NAudio.Wave;

namespace aBookPlayer;

/// <summary>
/// Decodes the supported audio formats (<see cref="AudioFormats"/>). Apart from OGG (NVorbis, ~100 KB), decoding
/// relies on what is built into NAudio or Windows (Media Foundation), so extra formats add no weight to the app.
/// </summary>
static class AudioDecoder
{
    /// <summary>Opens a seekable stream decoding to PCM/float. Can scan the whole file: call it off the UI thread.</summary>
    public static WaveStream Open(string path)
    {
        switch (Path.GetExtension(path).ToLowerInvariant())
        {
            case ".mp3":
                return new Mp3FileReader(path);
            case ".ogg":
                return new VorbisWaveReader(path);
            case ".aiff" or ".aif":
                return new AiffFileReader(path);
            case ".wav":
                var wav = new WaveFileReader(path);
                if (wav.WaveFormat.Encoding is WaveFormatEncoding.Pcm or WaveFormatEncoding.IeeeFloat)
                    return wav;
                // WAVE_FORMAT_EXTENSIBLE (24-bit/multichannel exports) is rejected by NAudio's sample
                // converters, and compressed WAVs (ADPCM, …) need a codec: let Windows decode both
                wav.Dispose();
                return new MediaFoundationReader(path);
            default:
                // M4A/M4B/AAC/MP4/WMA/FLAC: Windows' built-in decoders
                return new MediaFoundationReader(path);
        }
    }
}