Vienna-Budapest by train -seat reservation

I have bought tickets on line from Vienna to Budapest (using OBB website, by Railway). However, I have not booked a seat because I could take different trains depending of my arrival time to Vienna. So, I may take any train from Vienna to Budapest on 4th october, depending of my arrival time to Vienna, but I have not assigned a seat.

My question is: can I book a seat when I arrive at Vienna train station (Wien Meidling)? What must I do? Is there automatic machines to book the seat? Or I have to ask for it in the tickets office?

Really, is a great problem if I haven´t a seat booked for 4th october? (I think it´s not high season).

Hi - and welcome to Thron Tree.

If there is no compulsory requirement to reserve a seat, then don't worry about doing so.
I have taken the train many times from Vienna to Budapest (and back) - and 'Never' reserved a seat.
Sure, there were many seats reserved on the train, but also a lot free as well.
I would suggest boarding soon as the train arrives, rather than 2 minutes before it leaves.
You should be just fine - plus you're out of peak season too.
Best of luck with everything.

Thank you very much, battybilly!

You're very welcome ! !

you will get a seat without reservation, just be there maybe 15 minutes before departure