HDMI doesn't work like that-- there is no "blanking". That's also why there is no closed captioning in HDMI, It's all done at the source.
There are video data periods which is active video, and there are control periods and data island periods within the control periods. Audio is one of the things that can be in the data islands. The control periods/data periods can not be "passed through", they must be actively decoded in order to decode the video and manage the data flow.