STDOUTにstream_filter_append

gistfile1.php

<?php
$stream1 = fopen('php://output', 'wb');
stream_filter_append($stream1, 'string.rot13');
fwrite($stream1, "hoge\n");
fwrite(STDOUT, "hoge\n");
echo "hoge\n";

echo "-\n";

$stream2 = fopen('php://stdout', 'wb');
stream_filter_append($stream2, 'string.rot13');
fwrite($stream2, "hoge\n");
fwrite(STDOUT, "hoge\n");
echo "hoge\n";

echo "-\n";

stream_filter_append(STDOUT, 'string.rot13');
fwrite(STDOUT, "hoge\n");
echo "hoge\n";