// memcpy(play_buffer,    data_buffer, play_buffer_length); // works
// memcpy(play_buffer[],  data_buffer, play_buffer_length);
// memcpy(play_buffer[0], data_buffer, play_buffer_length);
// memcpy(&play_buffer,    data_buffer, play_buffer_length); // works
// memcpy(&play_buffer[],  data_buffer, play_buffer_length);
