Audio on web browser compatibility

Question

Wandering why the line "not supported by web browser" is in the code. It runs the audio if you try it.
<audio controls>
<source src="http://www.sololearn.com/uploads/audio.mp3" type="audio/mpeg">
<source src="http://www.sololearn.com/uploads/audio.ogg" type="audio/ogg">
Audio element not supported by your browser.
</audio>

Answer 1

In case it doesn't work, the message appears.

Answer 2

//Nicely Explained on audio lesson
https://www.sololearn.com/learn/HTML/2193/

Answer 3

Thanks!