PI3 HDMI and analog audio syncing issues

    Hi there!

    I've just started using LibreElec with a Raspberry PI 3 but already I'm really impressed with the out-of-box setup! Thumbs up!! I never even knew there was a HDMI-CEC functionality in Kodi, no more keyboard needed.... :)

    My specific setup at home, however, is causing some audio sync issues and I'm hoping somebody is able to help me because right now I'm stranded: I have a Onkyo TX-NR717 receiver. This receiver supports multiple rooms, however only non-hdmi (analog, internet radio) signals can be passed to room 2 and 3. My living room is room 1 and has a 5.1 setup and the kitchen is room 2 and has a 2.0 setup. The kitchen and living room are openly connected so if I want to enable sound in both rooms it is important they are synced. Because the receiver can only deliver an analog signal to the kitchen I've also connected the analog audio output of the PI to the analog in of the receiver and setup Kodi so it outputs audio to both HDMI and analog. This setup is working but with a minor delay on the hdmi stream (I think it is somewhere between 10 and 200 ms).

    After some Googling I think that there are 3 possible options to sync the audio:

    1. Buy a new receiver (The Onkyo one that is able to deliver hdmi signals to multiple rooms costs around 1500 dollars AFAIK, and even here I'm not sure the rooms are synced) No thank you....
    2. Delay the analog audio. I'm not sure this is a viable option because I don't know exactly how HDMI audio works, but I think there are 2 options:
      1. The delay between HDMI and analog is fixed. Delaying the analog audio with a fixed value should do the trick I hope.
      2. The delay is variable. Uhm... Well goodnight I guess.. ;(
    3. Use an HDMI audio extractor between the receiver and the PI HDMI to extract the audio and input it to the analog audio source on the receiver (again I'm not sure if this would still leave me with a syncing issue...)

    I'm really hoping somebody faced a similar issue and has a fix or workaround or knows if options 2 and 3 are even real options. My knowledge of HDMI signals is not that great (close to non-existent).

    Thank you in advance for any help!