How fast are you with the mouse, just visit some sites that embed music or auto-playing video and you will find out, as you rapidly click around trying to turn off the sound!
It is best when you use video or sound files to be courteous and to allow users to turn it off, turn it down, or even replay it. This is one reason why I do not like embedded background music that has no user controls. Typically a site that plays music onLoad is found to be annoying by most users. Sometimes it is an issue that the reader has their own music on, that they don’t like the music you have selected, that the music starts playing too loud, or even as they really review your site the music plays over and over forcing them to manually turn the sound off. Here’s one for you to check out that is a good example of why you should not have music embedded. It can be fatiguing to listen to the same clip over and over.
My tip for best practice is don’t embed background music in your website! If you do add sound files or videos be courteous and provide playback controls. Make sure to have the play, pause, and repeat buttons and consider not playing the video or sound on page load.