Generate .WAV from PCM (AWS Polly) - php

Question

I've tried to find answers online, but couldn't find anything that helped me...
I am trying to convert a PCM stream into a WAV file using PHP (7.2) and save it on the server.
Specifically, I am generating speech via Amazon Polly with the below code:
try {
$result = $client->synthesizeSpeech([
'Text' => 'Dies ist ein Test.',
'OutputFormat' => 'pcm',
'SampleRate' => '8000',
'VoiceId' => 'Hans'
]);
$resultData = $result->get('AudioStream')->getContents();
}
I need a WAV file for use with different code later on.
Many thanks for your help!

Answer 1

You just need to add a header and append the PCM data.
http://soundfile.sapp.org/doc/WaveFormat/
I couldn't find any PHP library for this, so I wrote a simple PHP program to do so:
<?php
$pcm = file_get_contents('polly.raw');
//$pcm = $result->get('AudioStream')->getContents();
//Output file
$fp = fopen('file.wav', 'wb');
$pcm_size = strlen($pcm);
$size = 36 + $pcm_size;
$chunk_size = 16;
$audio_format = 1;
$channels = 1; //mono
/**From the AWS Polly documentation: Valid values for pcm are "8000" and "16000" The default value is "16000".
* https://docs.aws.amazon.com/polly/latest/dg/API_SynthesizeSpeech.html#polly-SynthesizeSpeech-request-OutputFormat
**/
$sample_rate = 16000; //Hz
$bits_per_sample = 16;
$block_align = $channels * $bits_per_sample / 8;
$byte_rate = $sample_rate * $channels * $bits_per_sample / 8;
/**
* http://soundfile.sapp.org/doc/WaveFormat/
* https://github.com/jwhu1024/pcm-to-wav/blob/master/inc/wave.h
* https://jun711.github.io/aws/convert-aws-polly-synthesized-speech-from-pcm-to-wav-format/
**/
//RIFF chunk descriptor
fwrite($fp, 'RIFF');
fwrite($fp,pack('I', $size));
fwrite($fp, 'WAVE');
//fmt sub-chunk
fwrite($fp, 'fmt ');
fwrite($fp,pack('I', $chunk_size));
fwrite($fp,pack('v', $audio_format));
fwrite($fp,pack('v', $channels));
fwrite($fp,pack('I', $sample_rate));
fwrite($fp,pack('I', $byte_rate));
fwrite($fp,pack('v', $block_align));
fwrite($fp,pack('v', $bits_per_sample));
//data sub-chunk
fwrite($fp, 'data');
fwrite($fp,pack('i', $pcm_size));
fwrite($fp, $pcm);
fclose($fp);
You can use FFmpeg as well to achieve this, but my solution is purely written in PHP.
I hope I could help you!

Answer 2

PHP extension functions and/or classes that can be called from PHP scripts
https://www.php-cpp.com/documentation/functions
Simple Native wave file writer example:
https://www3.nd.edu/~dthain/courses/cse20211/fall2013/wavfile/