for (int i = 0; i < d.threads(); ++i) {
_threads.push_back (new boost::thread (boost::bind (&Encoder::encoder_thread, this, d)));
}
for (int i = 0; i < d.threads(); ++i) {
_threads.push_back (new boost::thread (boost::bind (&Encoder::encoder_thread, this, d)));
}