Unity3D: script to save an AudioClip as a .wav file.

SavWav.cs

//	Copyright (c) 2012 Calvin Rien
//        http://the.darktable.com
//
//	This software is provided 'as-is', without any express or implied warranty. In
//	no event will the authors be held liable for any damages arising from the use
//	of this software.
//
//	Permission is granted to anyone to use this software for any purpose,
//	including commercial applications, and to alter it and redistribute it freely,
//	subject to the following restrictions:
//
//	1. The origin of this software must not be misrepresented; you must not claim
//	that you wrote the original software. If you use this software in a product,
//	an acknowledgment in the product documentation would be appreciated but is not
//	required.
//
//	2. Altered source versions must be plainly marked as such, and must not be
//	misrepresented as being the original software.
//
//	3. This notice may not be removed or altered from any source distribution.
//
//  =============================================================================
//
//  derived from Gregorio Zanon's script
//  http://forum.unity3d.com/threads/119295-Writing-AudioListener.GetOutputData-to-wav-problem?p=806734&viewfull=1#post806734

using System;
using System.IO;
using UnityEngine;
using System.Collections.Generic;

public static class SavWav {

	const int HEADER_SIZE = 44;

	public static bool Save(string filename, AudioClip clip) {
		var filepath = Path.Combine(Application.persistentDataPath, filename);

		// Make sure directory exists if user is saving to sub dir.
		Directory.CreateDirectory(Path.GetDirectoryName(filepath));

		using (var fileStream = new FileStream(filepath, FileMode.Create)) {
			// ヘッダデータは後で記述するのでヘッダサイズ分シークする
			fileStream.Seek(HEADER_SIZE, SeekOrigin.Begin);
			MemoryStream memStream = new MemoryStream();
			ConvertAndWrite(memStream, clip);
			memStream.WriteTo(fileStream);
			WriteHeader(fileStream, clip);
		}

		return true; // TODO: return false if there's a failure saving the file
	}

	public static AudioClip TrimSilence(AudioClip clip, float min) {
		var samples = new float[clip.samples];

		clip.GetData(samples, 0);

		return TrimSilence(new List<float>(samples), min, clip.channels, clip.frequency);
	}

	public static AudioClip TrimSilence(List<float> samples, float min, int channels, int hz) {
		return TrimSilence(samples, min, channels, hz, false);
	}

	public static AudioClip TrimSilence(List<float> samples, float min, int channels, int hz, bool stream) {
		int i;

		for (i=0; i<samples.Count; i++) {
			if (Mathf.Abs(samples[i]) > min) {
				break;
			}
		}

		samples.RemoveRange(0, i);

		for (i=samples.Count - 1; i>0; i--) {
			if (Mathf.Abs(samples[i]) > min) {
				break;
			}
		}

		samples.RemoveRange(i, samples.Count - i);

		var clip = AudioClip.Create("TempClip", samples.Count, channels, hz, stream);

		clip.SetData(samples.ToArray(), 0);

		return clip;
	}

	static void ConvertAndWrite(MemoryStream memStream, AudioClip clip) {

		var samples = new float[clip.samples];
		clip.GetData(samples, 0);

		Int16[] intData = new Int16[samples.Length];
		//converting in 2 float[] steps to Int16[], //then Int16[] to Byte[]

		Byte[] bytesData = new Byte[samples.Length * 2];
		//bytesData array is twice the size of
		//dataSource array because a float converted in Int16 is 2 bytes.

		const int rescaleFactor = 32767; //to convert float to Int16

		for (int i = 0; i < samples.Length; i++)
		{
			intData[i] = (short)(samples[i] * rescaleFactor);
		}
		Buffer.BlockCopy(intData, 0, bytesData, 0, bytesData.Length);
		memStream.Write(bytesData, 0, bytesData.Length);
	}

	static void WriteHeader(FileStream fileStream, AudioClip clip) {

		var hz = clip.frequency;
		var channels = clip.channels;
		// samplesの値は
		var samples = clip.samples;
		const UInt16 bps = 16;

		fileStream.Seek(0, SeekOrigin.Begin);

		// 参考
		// http://www.web-sky.org/program/other/wave.php
		// http://sky.geocities.jp/kmaedam/directx9/waveform.html
		Byte[] riff = System.Text.Encoding.UTF8.GetBytes("RIFF");
		fileStream.Write(riff, 0, 4);

		Byte[] chunkSize = BitConverter.GetBytes(fileStream.Length - 8);
		fileStream.Write(chunkSize, 0, 4);

		Byte[] wave = System.Text.Encoding.UTF8.GetBytes("WAVE");
		fileStream.Write(wave, 0, 4);

		Byte[] fmt = System.Text.Encoding.UTF8.GetBytes("fmt ");
		fileStream.Write(fmt, 0, 4);

		// id と size を除くチャンクデータサイズ
		Byte[] subChunk1 = BitConverter.GetBytes(16);
		fileStream.Write(subChunk1, 0, 4);

		// 波形フォーマット(1=PCM)
		Byte[] audioFormat = BitConverter.GetBytes(1);
		fileStream.Write(audioFormat, 0, 2);

		// チャンネル数
		Byte[] numChannels = BitConverter.GetBytes(channels);
		fileStream.Write(numChannels, 0, 2);

		// サンプリング周波数(Hz)
		Byte[] sampleRate = BitConverter.GetBytes(hz);
		fileStream.Write(sampleRate, 0, 4);

		// バイトレート
		Byte[] byteRate = BitConverter.GetBytes(hz * channels * bps/8); // sampleRate * bytesPerSample*number of channels, here 44100*2*2
		fileStream.Write(byteRate, 0, 4);

		// データのブロックサイズ(１秒あたりの音声データのバイト数)
		UInt16 blockAlign = (ushort) (channels * bps/8);
		fileStream.Write(BitConverter.GetBytes(blockAlign), 0, 2);

		// 1 サンプルあたりのビット数
		Byte[] bitsPerSample = BitConverter.GetBytes(bps);
		fileStream.Write(bitsPerSample, 0, 2);

		// dataチャンク
		Byte[] datastring = System.Text.Encoding.UTF8.GetBytes("data");
		fileStream.Write(datastring, 0, 4);

		// dataのサイズ
		Byte[] subChunk2 = BitConverter.GetBytes(samples * channels * bps/8);
		fileStream.Write(subChunk2, 0, 4);
	}
}