The verb Boire is irregular in it's pronunciation. It most cases regular verbs for 1st, 2nd, 3rd, and 3rd person plural sound the same in the present infinitive.
Je mange, Tu manges, Il/Elle/on mange, Ils/Elles mangent <= All these sound the same when spoken.
In the particular case with Boire, 3rd person plural boivent has the "v" sound. 1st person, 2nd person and 3rd person singular sound the same except for 3rd person plural.
Another example is the verb Prendre. Je prends, tu prends, il/elle prend all sound the same. Except for the 3rd person plural: Ils/Elles prennent. With Je prend your lips make a sort of O shape, and with Ils prennent the corners of your mouth move farther apart.
"du" is the partitive article contracted from "de+le". It is used in front of a masculine singular noun starting with a consonant to mean "some".
"de la" is the feminine partitive article, to be used in front of a feminine, singular noun starting with a consonant to mean "some".
"de l' " is the masculine or feminine partitive article to be used in front of a noun starting with a vowel sound (vowel or non aspirate H).
It must've taken me 3 or for listenings before I caught the "v" sound in boivent. Which I thought meant plural which I didn't know how to hear in "il"
I had to make a guess and just assume it was "ils boivent"
second part I thought they said "du pain" which is bread and I knew bois meant drink. Drinking bread sounded wrong, so I realized they said "vin"
Everything connected and I got the answer right. It honestly took longer than necessary, but the journey was fun~ ^^
Since the French language does not have continuous tenses, "ils boivent du vin" can mean either "they are drinking wine" or "they drink wine". Context would tell which meaning it is.
However, when the French really want to describe an on-going action, they can say "ils sont en train de boire du vin", which exactly means "they are drinking wine".