Originally Posted by railways

I agree with this. To the OP - the journey planners will show the quickest journey from Salzburg to Venice as via Villach. This is a hybrid train and bus journey (the bus element taking 3-and-a-half hours), since daytime trains on the Villach - Tarvisio route were stopped a couple of years back. This is to be avoided unless you particularly like bus journeys. The all-train daytime routing (via Brenner) leaves Salzburg at 10:53 with one change at Innsbruck.

The scenery on both routes is pretty spectacular.