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How to Use the pack() Function to Generate a Standard WAV Audio File Header?

M66 2025-06-12

In audio programming, generating a standard WAV file header is a fundamental yet crucial step. WAV files are audio files based on the RIFF (Resource Interchange File Format) format, which is clear and easy to read. This article will manually construct a valid WAV file header using PHP's pack() function, helping developers gain a deeper understanding of the structure of the WAV format.

Basic Structure of a WAV File

A standard WAV file header can generally be divided into the following sections:

  1. RIFF Chunk: Marks the file as a RIFF file.

  2. WAVE Marker: Indicates that the file type is WAVE.

  3. fmt Subchunk: Contains audio format information (sampling rate, number of channels, bit depth, etc.).

  4. data Subchunk: Contains the actual audio data.

The structure is as follows:

| ChunkID | ChunkSize | Format |
|--------|-----------|--------|
| 'RIFF' | 36 + SubChunk2Size | 'WAVE' |
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<p>| Subchunk2ID | Subchunk2Size | Data |<br>

Using pack() to Construct the WAV Header

PHP's pack() function can pack data into a binary string, making it suitable for constructing the WAV file header. Below is a simple example of generating a 16-bit, mono, 44.1kHz WAV file header, assuming the audio data size is $dataSize bytes:

<?php
<p>function createWavHeader($dataSize, $sampleRate = 44100, $bitsPerSample = 16, $channels = 1)<br>
{<br>
$byteRate = $sampleRate * $channels * $bitsPerSample / 8;<br>
$blockAlign = $channels * $bitsPerSample / 8;<br>
$header = '';</p>
$header .= pack('A4', 'RIFF');                              // ChunkID
$header .= pack('V', 36 + $dataSize);                       // ChunkSize
$header .= pack('A4', 'WAVE');                              // Format

// fmt Subchunk
$header .= pack('A4', 'fmt ');                              // Subchunk1ID
$header .= pack('V', 16);                                   // Subchunk1Size
$header .= pack('v', 1);                                    // AudioFormat (1 = PCM)
$header .= pack('v', $channels);                            // NumChannels
$header .= pack('V', $sampleRate);                          // SampleRate
$header .= pack('V', $byteRate);                            // ByteRate
$header .= pack('v', $blockAlign);                          // BlockAlign
$header .= pack('v', $bitsPerSample);                       // BitsPerSample

// data Subchunk
$header .= pack('A4', 'data');                              // Subchunk2ID
$header .= pack('V', $dataSize);                            // Subchunk2Size

return $header;

}

// Example: Write an empty WAV file
$dataSize = 44100 * 2 * 1; // 1 second of mono 16-bit audio data
$header = createWavHeader($dataSize);
file_put_contents('output.wav', $header . str_repeat("\x00", $dataSize));

echo "WAV file created. You can download the test file from m66.net.";

Explanation of Parameters

  • $sampleRate: The sample rate, common values include 44100, 48000, etc.

  • $bitsPerSample: The bit depth of each sample, typically 8 or 16.

  • $channels: The number of channels, 1 for mono, 2 for stereo.

  • $dataSize: The actual byte size of the audio data, calculated as: duration * sample rate * number of channels * bit depth / 8.

Use Cases

Using pack() to construct the WAV file header is ideal for the following scenarios:

  • Server-side dynamic generation of audio streams.

  • Export of custom audio recording formats.

  • Development of data compression and audio packaging analysis tools.

Conclusion