replicate openssl encrypt/decrypt between PHP and Command Line for large files?

Question

I am trying to create a PHP method to replicate the OpenSSL command line function so I can encrypt using the command line and then decrypt it using PHP or the opposite by encrypting using PHP and then decrypting using the command line.

i created this PHP method for encrypting files:

$salt= random_bytes(8);
$saltPrefix = "Salted__" . $salt;
$keyIV= EVP_BytesToKey($salt, file_get_contents('my.key'));
$key = substr($keyIV, 0, 32);
$original = file_get_contents('confidential.txt');
$encrypted = openssl_encrypt($original, 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);
file_put_contents('php-encrypted.bin', $saltPrefix . $encrypted);

then after running this method, I can decrypt it using this command line:

openssl  enc -p -d -aes-256-cbc -in php-encrypted.bin -out decrypted.txt -pass file:my.key

but there is a problem when the file to encrypt is large so I try to update the above PHP method to don't get memory limit issue:

$FILE_ENCRYPTION_BLOCKS = 64;
if ($fpOut = fopen('php-encrypted.bin', 'w')) {
    fwrite($fpOut, $saltPrefix);
    if ($fpIn = fopen('confidential.txt', 'rb')) {
        while (!feof($fpIn)) {
            $plaintext = fread($fpIn, 16 * $FILE_ENCRYPTION_BLOCKS);
            $encrypted = openssl_encrypt($plaintext, 'AES-256-CBC', $key, OPENSSL_RAW_DATA, $iv);
            fwrite($fpOut, $encrypted);
        }
        fclose($fpIn);
    }
    fclose($fpOut);
}

but when i try to decrypt the generated file as before using the command line it is not working. i need to update the above method to follow memory performance issue but want to keep it able to be encrypted using command line like the original method.