Which army and unit?

Dear all,

I don't know much about the WWI experience of my grandfather, Richard Gaensler, as he never talked to his family about it. All I have are these two photos - one taken during the war and another some time after.

Can someone tell me which army and unit he might have been in (or even what rank), based on the uniforms and medals he is wearing? He was born in Vienna and probably was fighting for Austria-Hungary, but possibly also for Germany.

many thanks in advance for your thoughts,

Bryan Gaensler

Bryan,
The collar badge looks like that of the Automobile troops.
Looking at the rank badge they seem to be of officer quality which would make his rank Oberleutnant, if not, then its Korporal.
The first picture looks more like an NCO's uniform but there appears to be a button on the collar tab, this would make it an officers greatcoat.
Also, if it was taken during the war many officers dressed down for self preservation.
Someone with better eyes and more knowledge may be able to be of greater help.
Regards
WF