How does a HDMI handshake work?

[Trevor]

I have a question about HDMI that I can’t post in the Tech Talk forum as I don’t have the privileges.

I am trying to resolve an HDMI issue between my Mac Mini and my LG TV, which I use as a second display. The interface between the two works fine if I use a USB-C port and an HDMI adapter.

However, when I use the HDMI port on the computer it does not recognize the TV consistently. I have tried talking to Apple support, but they blame the TV. There are many others out there with the same issue on many other different TVs.

Before I get into any specifics, could someone direct me to somewhere that I could learn how the HDMI handshake works? I would like to understand more before I start asking detailed questions.

 

[tripplej]

See this link to learn more about hdmi --> https://electronics.howstuffworks.com/hdmi.htm

See this link for troubleshooting -> https://www.lifewire.com/fix-hdmi-connection-problems-1846811

Not sure which LG model you have but you may want to look at this one setting that is set off to resolve his issue in the video --

 

[Trevor]

Hi trippleJ,

Thank you for your reply, I have read the links you listed. That one particular TV setting did not resolve it for me.

I do not have a consistent set of symptoms to give you, but the TV is intermittently recognized through the HDMI port whereas the TV is always recognized through the USB-C port (with HDMI adapter).

My gut feeling is that the HDMI handshake between the two fails, and is not reattempted. I believe it is supposed to keep trying, and maybe it is but I don't know how to tell. How often should the handshake be occuring, and which unit sends the invitation to communicate; the computer or the TV?

 

[gp4Jesus]

Thanks for starting this thread.

I’m trying to hack a manual “single HDMI in double HDMI output” switch, so on power up, my pre/pro trigger will switch for me. It’s complicated, too complicated to explain right now.

Tony

 

[thothsong]

The HDCP protocol is initiated by the source device. In case of failure, the source "must retry periodically, with a period of no more than 2 seconds (preferably much more often)". You can read the HDCP 2.3 specification if you want full details.