Breakdown of Ég hlusta á hljóðbók í strætó, jafnvel þegar ég er þreyttur.
Questions & Answers about Ég hlusta á hljóðbók í strætó, jafnvel þegar ég er þreyttur.
Because hlusta is one of those Icelandic verbs that normally takes the preposition á with the thing you are listening to.
So Icelandic says:
hlusta á tónlist = listen to music
hlusta á hljóðbók = listen to an audiobook
This is something you largely have to learn with the verb. The á here is not the ordinary location word on; it is just the preposition that belongs with hlusta.
It is in the accusative, because hlusta á takes an accusative object.
So in Ég hlusta á hljóðbók, the noun after á is accusative.
A useful detail: hljóðbók is a feminine noun, and in the singular its nominative and accusative forms are the same, so you do not see any visible change here. That is why it still looks just like the dictionary form.
Icelandic does not have a separate indefinite article like English a/an.
So:
hljóðbók can mean an audiobook or audiobook, depending on context.
If you wanted the audiobook, Icelandic would usually add the definite article to the end of the noun:
hljóðbókin = the audiobook
So the sentence uses the plain indefinite form: hljóðbók.