Frustrating, but part of learning. The audio is fine. (I listened to it and asked my son to listen to it without telling him what it was supposed to say.) It takes times for your ears to get used to the sounds of a new language.
kantas can mean either "sing" or "are singing". You can use the present progressive form -ant if you absolutely need it for some reason (which you'll learn much later), but usually this simple form is used and can be either simple or progressive.
I know nothing about this but you've been learning a lot of language a I see, so you must know this is something quite unique from the english language. Have you tumbled upon a similar form in any of those languages you learned?
well, I'm assuming this probably means "are singing" in the way that Spanish, French, others use simple present tense. But some languages have specific present progressive forms (likes Spanish-- estoy cantando -I am singing. Canto - I sing.)
This is a constructed language designed to have no conjugations and no irregularities. It doesn't mean the tenses are absent. You'll notice that all adjectives end in the same ending and all nouns end in the same ending etc.