PHP FFmpeg: Parse and convert SILK audio format

FFmpeg is an open source multimedia framework capable of parsing and converting almost all common audio and video formats. Therefore, it is also one of the preferred tools for parsing and converting audio or video using PHP. This article explains how to use PHP and the FFmpeg extension to parse and convert the SILK audio format.

What is SILK?

SILK is a special audio codec (codec) format used by Skype for VoIP calls. This codec is widely used in Skype and is also used by several other messaging applications. Since SILK is not supported by default in Linux or Unix, we need to use FFmpeg to handle it.

Installing FFmpeg

Before you begin, make sure you have installed FFmpeg and related extensions. If not, please install it using the following command on a Linux or Unix system:

sudo apt-get update
sudo apt-get install ffmpeg php-ffmpeg

Parsing SILK

To parse a SILK file into other common audio formats, you first need to use FFmpeg to decode the SILK file. Before executing FFmpeg commands through PHP, please read the FFmpeg documentation carefully to ensure that you are familiar with the usage.

When using the FFmpeg extension in PHP, you can open the audio file using the open() method of the FFMpeg\FFMpeg class. This method returns a FFMpeg\Media\Audio object, which can access various properties and information of the audio and perform arbitrary processing.

The following is a sample code for parsing a SILK file through PHP:

require_once('vendor/autoload.php');
use FFMpeg\FFMpeg;
$ffmpeg = FFMpeg::create();
$audio = $ffmpeg->open('input.silk');
$format = $audio->getFormat();
$codec = $format->getAudioCodec();
// Do something with the audio file...

In the code example, the open() method is used to open the SILK file. $format->getAudioCodec() The method is used to get the name of the audio codec, usually "silk".

Convert SILK

When converting a SILK file, you need to first decode it to PCM format and then encode the PCM via FFmpeg. Use the FFmpeg command ffmpeg -f s16le -ar 24000 -ac 1 -i input.pcm -codec:a libmp3lame -qscale:a 4 output.mp3 to convert the content from PCM to MP3 (or other formats) .

The following is a sample code to convert a SILK file to MP3 using PHP:

require_once('vendor/autoload.php');
use FFMpeg\FFMpeg;
$ffmpeg = FFMpeg::create();
$audio = $ffmpeg->open('input.silk');
$format = $audio->getFormat();
$codec = $format->getAudioCodec();
if ($codec === 'silk') {
    // Decode SILK to PCM
    $temp_file = tempnam(sys_get_temp_dir(), 'php-silk');
    exec("ffmpeg -i input.silk -acodec pcm_s16le -ar 24000 -ac 1 -f s16le $temp_file");
    $audio = $ffmpeg->open($temp_file);
    // Encode PCM to MP3
    $format = new \FFMpeg\Format\Audio\Mp3();
    $format->setAudioCodec("libmp3lame");
    $format->setAudioQuality(4);
    $audio->save($format, "output.mp3");
    unlink($temp_file);
}

The above code first checks if the codec is SILK, and if so, decodes to PCM format. Then, use FFMpeg\Format\Audio\Mp3() to create an MP3 format object and save it as a file.

Summary

The FFmpeg extension is a powerful tool to parse and convert audio or video in PHP. In this article, we show how to parse and convert the SILK audio format using PHP and the FFmpeg extension. This will help developers easily convert SILK files to other common audio formats to suit their needs.

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