Can I use a famous song in a video I upload online?

Music is protected by copyright, and using a recording of a song, even a short excerpt, without a licence can infringe copyright in both the musical composition and the sound recording. There is no fixed number of seconds that is automatically permitted. The Copyright Act 1994 does allow certain fair dealing, for criticism, review, news reporting, research or private study, but using music merely as background in a commercial video would not normally qualify. Online platforms often have their own licensing arrangements and can remove content, mute audio or demand payment. To be safe, use music that is licensed for commercial use, royalty-free libraries with clear terms, or seek a licence from the rights holders or the collecting societies that represent them. Keep proof of your licences.