When inserting audio into the video stream via APx_IN pins
If ADV7623 is powered up, the I2S source can be powered or not powered without issue
If ADV7623 is powered off, the I2S source should be set to low values or tri-stated
When extracting audio from the video stream via APx_OUT pins
If I2S sink is powered up, the ADV7623 APx_OUT pins can be powered or not powered without issue
if I2S sink is powered off, the ADV7623 APx_OUT pins should be tri-stated
I am assuming we are talking about supply timing here.