<form method="post" name="post_form" action="conversion.php" enctype="multipart/form-data">
    <input type="file" name="voice">
    <input type="submit" name="btnUpload" value="submit">
</form>
<?php
    if($_POST['btnUpload']) {
        $username = "username";
        $password = "password";
        $url = 'https://stream.watsonplatform.net/speech-to-text/api/v1/recognize?continuous=true&model=en-US_NarrowbandModel';
        $filename = $_FILES['voice']['name'];
        $filedata = $_FILES['voice']['tmp_name'];
        $file = fopen($filename, 'r');
        $filesize = filesize($filename);
        $bytes = fread($file,$filesize);
        $data = array('part_content_type' => 'audio/flac');
        $headers = array("Content-Type: audio/flac", "Transfer-Encoding: chunked");
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_USERPWD, "$username:$password");
        curl_setopt($ch, CURLOPT_POST, TRUE);
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        curl_setopt($ch, CURLOPT_BINARYTRANSFER, TRUE);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $bytes);
        curl_setopt($ch, CURLOPT_INFILESIZE, $filesize);
        curl_setopt($ch, CURLOPT_VERBOSE, true);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        $executed = curl_exec($ch);
        curl_close($ch);
        var_dump($executed); exit;
    }

?>