Only works for English songs. I searched for a Pakistani song as famous as national anthem ("dil dil Pakistan"). It couldn't find it.

I was thinking it learns the tune of song and matches with that so language should not matter.

It worked for "Desert Rose" though.

Edit: Also worked for an Indian song.

Also worked for few other recent famous Pakistani songs. I guess the first song that I searched is probably not listened on YouTube as much as its known by heart.

It could not search for national anthem itself for the reason.