How many days do you need to play around Salzburg and Vienna ?

It's hard to say, it depends on what you want to do. Generally, Salzburg for two or three days, Vienna for three days.

Salzburg, not only Salzburg, but also Wolfgang and Hallstatt these lake area towns, it is suggested to stay for more than three days. Vienna normally needs two days. In my opinion, the essence of Austria is in these two places. Deep travel in Salzburg and its surroundings, on the one hand you can search for the footprints of the Sound of Music, on the other hand the scenery is comparable to that of Switzerland, especially when you drive and stop along the way to enjoy the scenery. Because Vienna is relatively large and has many museums, two days are basically enough.