是否可以使用 PHP 生成 WAV 文件？

Posted 2023-02-24

【中文标题】是否可以使用 PHP 生成 WAV 文件？

【英文标题】：Is it possible to generate WAV files using PHP?

【发布时间】：2019-05-10 22:03:13

【问题描述】：

我想编写一个生成短音频文件（最好是 WAV）的小型 Web 应用程序。

音频文件会很简单，像这样：

例如。用户输入：

350 1000
500 1000

输出：两秒 WAV 文件，第一秒为 350Hz 音调，第二秒为 500Hz 音调，如this generator。

是否可以使用 php 来做到这一点？

【问题讨论】：

你可能需要搜索一个 php 插件来生成音频文件。

【参考方案1】：

WAV 文件格式非常简单，您可以使用 PHP 从头开始​​编写 WAV 文件，前提是您只想输出可以通过编程轻松生成的简单波形。

这是一个使用您发布的输入格式将正弦波写入 8 位 44.1kHz 文件的示例。我使用以下内容作为参考：

Intro to Audio Programming, Part 2: Demystifying the WAV Format

A simple C# Wave editor, part 1: Background and analysis

<?php
/*
 * Set some input - format is [Hz, milliseconds], so [440, 1000] is 440Hz (A4) for 1 second
 */
$input = [
    [175, 1000],
    [350, 1000],
    [500, 1000],
    [750, 1000],
    [1000, 1000]
];

//Path to output file
$filePath = 'test.wav';

//Open a handle to our file in write mode, truncate the file if it exists
$fileHandle = fopen($filePath, 'w');

// Calculate variable dependent fields
$channels = 1; //Mono
$bitDepth = 8; //8bit
$sampleRate = 44100; //CD quality
$blockAlign = ($channels * ($bitDepth/8));
$averageBytesPerSecond = $sampleRate * $blockAlign;

/*
 * Header chunk
 * dwFileLength will be calculated at the end, based upon the length of the audio data
 */
$header = [
    'sGroupID' => 'RIFF',
    'dwFileLength' => 0,
    'sRiffType' => 'WAVE'
];

/*
 * Format chunk
 */
$fmtChunk = [
    'sGroupID' => 'fmt',
    'dwChunkSize' => 16,
    'wFormatTag' => 1,
    'wChannels' => $channels,
    'dwSamplesPerSec' => $sampleRate,
    'dwAvgBytesPerSec' => $averageBytesPerSecond,
    'wBlockAlign' => $blockAlign,
    'dwBitsPerSample' => $bitDepth
];

/*
 * Map all fields to pack flags
 * WAV format uses little-endian byte order
 */
$fieldFormatMap = [
    'sGroupID' => 'A4',
    'dwFileLength'=> 'V',
    'sRiffType' => 'A4',
    'dwChunkSize' => 'V',
    'wFormatTag' => 'v',
    'wChannels' => 'v',
    'dwSamplesPerSec' => 'V',
    'dwAvgBytesPerSec' => 'V',
    'wBlockAlign' => 'v',
    'dwBitsPerSample' => 'v' //Some resources say this is a uint but it's not - stay frosty.
];


/*
 * Pack and write our values
 * Keep track of how many bytes we write so we can update the dwFileLength in the header
 */
$dwFileLength = 0;
foreach($header as $currKey=>$currValue)

    if(!array_key_exists($currKey, $fieldFormatMap))
    
        die('Unrecognized field '.$currKey);
    

    $currPackFlag = $fieldFormatMap[$currKey];
    $currOutput = pack($currPackFlag, $currValue);
    $dwFileLength += fwrite($fileHandle, $currOutput);


foreach($fmtChunk as $currKey=>$currValue)

    if(!array_key_exists($currKey, $fieldFormatMap))
    
        die('Unrecognized field '.$currKey);
    

    $currPackFlag = $fieldFormatMap[$currKey];
    $currOutput = pack($currPackFlag, $currValue);
    $dwFileLength += fwrite($fileHandle, $currOutput);


/*
 * Set up our data chunk
 * As we write data, the dwChunkSize in this struct will be updated, be sure to pack and overwrite
 * after audio data has been written
 */
$dataChunk = [
    'sGroupID' => 'data',
    'dwChunkSize' => 0
];

//Write sGroupID
$dwFileLength += fwrite($fileHandle, pack($fieldFormatMap['sGroupID'], $dataChunk['sGroupID']));

//Save a reference to the position in the file of the dwChunkSize field so we can overwrite later
$dataChunkSizePosition = $dwFileLength;

//Write our empty dwChunkSize field
$dwFileLength += fwrite($fileHandle, pack($fieldFormatMap['dwChunkSize'], $dataChunk['dwChunkSize']));

/*
    8-bit audio: -128 to 127 (because of 2’s complement)
 */
$maxAmplitude = 127;

//Loop through input
foreach($input as $currNote)

    $currHz = $currNote[0];
    $currMillis = $currNote[1];

    /*
     * Each "tick" should be 1 second divided by our sample rate. Since we're counting in milliseconds, use
     * 1000/$sampleRate
     */
    $timeIncrement = 1000/$sampleRate;

    /*
     * Define how much each tick should advance the sine function. 360deg/(sample rate/frequency)
     */
    $waveIncrement = 360/($sampleRate/$currHz);

    /*
     * Run the sine function until we have written all the samples to fill the current note time
     */
    $elapsed = 0;
    $x = 0;
    while($elapsed<$currMillis)
    
        /*
         * The sine wave math
         * $maxAmplitude*.95 lowers the output a bit so we're not right up at 0db
         */
        $currAmplitude = ($maxAmplitude)-number_format(sin(deg2rad($x))*($maxAmplitude*.95));

        //Increment our position in the wave
        $x+=$waveIncrement;

        //Write the sample and increment our byte counts
        $currBytesWritten = fwrite($fileHandle, pack('c', $currAmplitude));
        $dataChunk['dwChunkSize'] += $currBytesWritten;
        $dwFileLength  += $currBytesWritten;

        //Update the time counter
        $elapsed += $timeIncrement;
    


/*
 * Seek to our dwFileLength and overwrite it with our final value. Make sure to subtract 8 for the
 * sGroupID and sRiffType fields in the header.
 */
fseek($fileHandle, 4);
fwrite($fileHandle, pack($fieldFormatMap['dwFileLength'], ($dwFileLength-8)));

//Seek to our dwChunkSize and overwrite it with our final value
fseek($fileHandle, $dataChunkSizePosition);
fwrite($fileHandle, pack($fieldFormatMap['dwChunkSize'], $dataChunk['dwChunkSize']));
fclose($fileHandle);

这是一个概念证明，说明了如何根据您的输入创建文件，使其在 Web 应用程序中工作取决于您。