To the sounds effects masking the audio, even though my videos have the game sound effects turned up YT manages to detect the song playing sometimes. They clearly have quite a clever system (or a human for that matter).
Regarding visual effects, the intro doesn't really pose much of a point rather than having a play with the effects you can make. For that matter you might as well make a short 5s clip of your effect and upload that on it's own to show what you made.