In the United States, works published with a copyright notice from 1923 through 1977 are protected for 95 years from the date of publication. Those published in 1978 or thereafter are now protected for 70 years after the death of the creator, as are those in the European Community. In Canada and other countries the period is life plus 50 years.I can't say I got more wiser from this except that it's tricky to know what's what. Since I'm European I've grown up with the rule being 70 years after the maker's death and knowing that even after that you can't use a song or image however you want. In Sweden we have something called 'Klassikerskyddet' which directly means 'Protection of classics' - it still protect, in a sense, a piece of work even after those 70 years.
In the same article as the above quote comes from I got this:
[...] Swan Lake is no longer under copyright and this public domain music can be freely used without seeking permission from a publisher. In other words you don't have to pay anyone to acquire synchronization rights to be able to use the music of Swan Lake.Like I thought then, so if my friend hire a Symphonic orchestra to play the song for him then it's all good, or he can do the easy way and contact the company who made the version he used. He will probably use it without doing neither, like everybody else though. It conjures an interesting thought: how many of us violate copyright laws on a daily basis without knowing it?
However, if you use an existing recording of Swan Lake in your work, that recording is protected by copyright and you would need to get permission from the record company to use it.
Source: The public domain and and a guide to media producers by John Bickerton