The Offline mode was added to Bidule so that it could be used to
You cannot use an audio device (input or output) in Offline mode. In almost all cases, you will use an Audio File Recorder bidule (or more than one) instead to record the offline output.
When using the Offline mode, you will notice that the standard cpu gauge has been replaced by an elapsed time meter, which should give you an estimate of the speed at which the render is done.