What are the disadvantages of mp4?

The disadvantages of MP3's are that MP3 player's headphones or earphone contain pieces of magnet. When the music you're playing, release an ultrasonic tone, which bounces to your ear drums, this is very dangerous and could seriously damage your ears. People have also been known to have been run over when running or walking with an MP3 in as you cannot hear traffic coming while crossing the road, this happens because the music can shut you off from the rest of the world.