A guide to audio manipulation in PHP

As a widely used server-side language, PHP plays an important role in many web applications. Audio processing is a very common requirement, such as music websites and audio product sales websites. In this article, readers will be introduced to how to operate audio files in PHP.

1. Understand the audio format

Before operating audio files in PHP, you need to first understand the audio file format. Common audio formats include MP3, WAV, OGG, FLAC, etc. Different formats have different audio encoding algorithms and data formats. For example, the MP3 format uses a lossy compression algorithm that can reduce file size while maintaining high audio quality. However, the MP3 format may result in loss of original audio data due to lossy compression.

In PHP, the use of extension libraries can support the processing of multiple audio formats. For example, to process audio files in MP3 format, you need to use PHP's ID3 extension or the PHP audio extension. For audio files in WAV format, you can use PHP's Wave extension. Files in OGG format can be processed through the Vorbis extension.

2. Reading and writing of audio files

Generally speaking, reading audio files is to process the audio data in the file, and writing audio files is to process the processed audio files. The audio data is stored in a file. In PHP, different extension libraries can be used to accomplish these operations.

1. Read audio files

The PHP audio extension provides the ability to read audio files. You can use the audioread function to read data from audio files. The following is a sample code that reads an audio file in MP3 format:

$audio_file = 'test.mp3';
$audio_data = audioread($audio_file);

This code will read an audio file named test.mp3 and store it in the $audio_data variable. This function returns an array containing all audio data.

2. Writing audio files

The PHP audio extension also provides the ability to write audio files. You can use the audiowrite function to write audio data to a specified audio file. The following is a sample code that writes audio data to a WAV format file:

$audio_file = 'test.wav';
$audio_data = array(0.5, 0.6, 0.3, -0.4, -0.2);
audiowrite($audio_file, $audio_data, $sample_rate = 44100);

This code will create an audio file named test.wav and write the data in the array $audio_data to the file . The $sample_rate parameter specifies the audio sampling rate.

3. Audio data processing

Once the audio file is read, the audio data can be processed, such as audio editing, audio mixing, etc.

1. Audio clipping

Audio clipping refers to the interception of audio data. You can use the array_slice function to complete the audio clipping operation, for example:

$audio_data = array(0.5, 0.6, 0.3, -0.4, -0.2);
$clip_data = array_slice($audio_data, 1, 3);

This code will clip the 2nd to 4th samples of the $audio_data array and store them in the $clip_data array.

2. Audio Mixing

Audio mixing refers to the merging operation of multiple audio files. Audio mixing can be done using the audiomix function provided in PHP's audio extension. For example:

$audio_file1 = 'test1.wav';
$audio_file2 = 'test2.wav';
$mix_file = 'mix.wav';

$data1 = audioread($audio_file1);
$data2 = audioread($audio_file2);

$mix_data = audiomix(array($data1, $data2));

audiowrite($mix_file, $mix_data);

This code will read the audio data of the two files test1.wav and test2.wav, mix them together, and write the mixed data to the mix.wav file.

4. Audio data calculation

In addition to simple audio processing operations, audio data calculation operations can also be performed in PHP. For example, using the FFT library that calculates the fast Fourier transform, you can calculate the spectral value, frequency, energy and other information of audio data.

1. Calculating spectrum values

Calculating the spectrum values ​​of audio data is one of the common requirements for audio analysis. You can use PHP's FFT library to perform fast Fourier transform to obtain the spectrum value of the audio data. For example:

$audio_file = 'test.wav';
$audio_data = audioread($audio_file);

$spectrum = fft($audio_data);

This code will read the audio data of the test.wav file, calculate the spectrum value of the audio data using the FFT library, and then store the result in the $spectrum variable.

2. Calculate Frequency

One of the methods used to calculate frequency is to find the value of the dominant frequency in the audio data. Dominant frequency refers to the strongest frequency in an audio signal and is commonly used in applications such as audio recognition and automatic song tagging. You can use PHP's FFT library to calculate the frequency of audio data, for example:

$audio_file = 'test.wav';
$audio_data = audioread($audio_file);

$spectrum = fft($audio_data);

$max_spectrum = max($spectrum);
$max_key = array_search($max_spectrum, $spectrum);
$sample_rate = 44100;
$freq = $max_key/$sample_rate;

This code will read the audio data of the test.wav file and use the FFT library to calculate the spectrum value of the audio data. Then, find the largest spectrum value in the result and calculate its corresponding frequency value.

5. Conclusion

This article introduces the method of using the extension library to read, write, process and calculate audio files in PHP. By studying this article, readers can understand the basic knowledge of PHP in audio processing and start writing PHP-based audio applications.

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