Is there a way to not show the player but just play the mp3 file?

Try to move it out of the screen with CSS. But i am not sure that it will work. Really why you want to do this?

I have a sound byte (speech) that I want to play when someone comes to the site but I don;t want the player to be visible.

I have a sound byte (speech) that I want to play when someone comes to the site but I don;t want the player to be visible.

Since it would be just in your home page, i suggest to use a custom script for that and not AllVideos. I am pretty sure that if you search using Google you will find the answer. Regarding AllVideos, as i said you can do it probably with CSS but it will affect all your site videos.