First, you can read Andrew's suggestion (as a comment). Then you need to ask two different questions because each case is different.
For the first one, "melody in my head", specify the genre, featuring "special" instruments, approximate date when it was trending, the language, the country, which media. Maybe you van remember a few lyrics...? Any detail matter and here you will find a list of relevant details. Then you can eventually add a recording of you humming the song, or play it in an instrument, or an online sequencer.
Obviously the melody won't be useful
I disagree with that. Any detail matter and could eventually ring a bell to someone. There is no reason to hide a detail if remembered.
For the second one, "plot of the video", try to remember which media, country etc... please try to remember something about the actual music. ID questions with no music details are often closed.