Base64 decode is used when binary data is shipped across a network, because some protocols may interpret data as control character or data can be corrupted when the protocol intepret data as special character combination. So, when data is transfered thru a protocol it's better if you encode data before transmiting and decode it after receiveing.
string base64_decode ( string $data [, bool $strict = false ] );
$data - The encoded data.
$strict - Returns FALSE if input data contains characters outside the base64 alphabet.
Returns the original e.g decoded data.
Returns FALSE on failure.
$decode = 'Q29kZSBCZWF1dGlmeQ==';
Base64.decode64 ( data )
data - Data that needs to be decoded.
Returns base64 decoded data ignoring characters outsite base alphabet.
data = 'Q29kZSBCZWF1dGlmeQ=='
decoded_data = Base64.decode64(data)