swift-cli/Sources/AudioIO.swift

import Foundation

/// Writes audio samples to a 16-bit PCM WAV file.
func writeWAV(_ samples: [Float], to url: URL, sampleRate: Int = 24_000) throws {
    let numSamples = samples.count
    let dataSize = numSamples * 2  // 16-bit PCM
    var data = Data()

    // RIFF header
    data.append(contentsOf: "RIFF".utf8)
    var chunkSize = UInt32(36 + dataSize).littleEndian
    data.append(Data(bytes: &chunkSize, count: 4))
    data.append(contentsOf: "WAVE".utf8)

    // fmt chunk
    data.append(contentsOf: "fmt ".utf8)
    var fmtSize = UInt32(16).littleEndian; data.append(Data(bytes: &fmtSize, count: 4))
    var audioFormat = UInt16(1).littleEndian; data.append(Data(bytes: &audioFormat, count: 2))
    var channels = UInt16(1).littleEndian; data.append(Data(bytes: &channels, count: 2))
    var sr = UInt32(sampleRate).littleEndian; data.append(Data(bytes: &sr, count: 4))
    var byteRate = UInt32(sampleRate * 2).littleEndian; data.append(Data(bytes: &byteRate, count: 4))
    var blockAlign = UInt16(2).littleEndian; data.append(Data(bytes: &blockAlign, count: 2))
    var bitsPerSample = UInt16(16).littleEndian; data.append(Data(bytes: &bitsPerSample, count: 2))

    // data chunk
    data.append(contentsOf: "data".utf8)
    var dataChunkSize = UInt32(dataSize).littleEndian; data.append(Data(bytes: &dataChunkSize, count: 4))
    for sample in samples {
        let clamped = max(-1.0, min(1.0, sample))
        var pcm = Int16(clamped * 32767.0).littleEndian
        data.append(Data(bytes: &pcm, count: 2))
    }

    try data.write(to: url)
}