Learn Hardcore Portuguese (Portugal): Prometo devolver os auscultadores assim que acabar o vídeo. - I promise to return the headphones as soon as I finish the video.

Portuguese is a null‑subject language. The verb ending in prometo already shows 1st‑person singular, so eu is optional unless you want emphasis (e.g., Eu prometo…).

What is the form in assim que acabar, and why not acabe or vai acabar?

It’s the future subjunctive, used after temporal conjunctions like assim que, quando, logo que, mal when referring to the future. Example forms: quando eu acabar, tu acabares, ele/ela acabar, nós acabarmos, eles/elas acabarem. You don’t use the present subjunctive (acabe) or a periphrastic future (vai acabar) in this context.

Who is the subject of acabar here—me or the video?

It can be ambiguous because the 1sg and 3sg of the future subjunctive are both acabar. Context usually tells you it’s “I finish the video.” To make it explicit:

As soon as I finish the video: assim que eu acabar o vídeo / assim que acabar de ver o vídeo.
As soon as the video ends: assim que o vídeo acabar.

Can I use quando instead of assim que?

Yes. Assim que means “as soon as,” emphasizing immediacy. Quando just means “when.” Both take the future subjunctive for future time: assim que/quando acabar o vídeo.

What about logo que or mal?

Both are good in Portugal:

logo que ≈ “as soon as,” slightly more formal/written.
mal
- future subjunctive is idiomatic: Mal acabar o vídeo, devolvo os auscultadores = “As soon as I finish the video.”

Why devolver and not entregar or voltar?

devolver = return something to its owner.
entregar = hand in/hand over (to whoever should receive it).
voltar = to return (someone goes back), not for returning an object.

Is auscultadores really “headphones”? Isn’t auscultador a stethoscope?

In European Portuguese, auscultadores (plural) is the standard word for headphones. Singular auscultador commonly refers to a stethoscope. For earbuds/in‑ear types many say auriculares. In Brazil, people say fone(s) de ouvido.

Why is it plural os auscultadores?

Like English “headphones,” Portuguese treats them as a pair. The plural is normal. The singular can mean one earpiece—or, in EP, a stethoscope.

Could I replace os auscultadores with “them”? Where does the pronoun go?

With the infinitive: Prometo devolvê‑los assim que acabar o vídeo. (enclisis to the infinitive)
With a finite clause: Prometo que os devolvo assim que acabar o vídeo. (proclisis after que is standard in EP)

Why is it o vídeo (definite)? Could I say um vídeo?

O vídeo refers to a specific video (the one you’re watching). Um vídeo would be nonspecific and is unusual in this context unless that’s what you mean.

Is the word order assim que acabar o vídeo normal? Can I say assim que o vídeo acabar?

Both are correct. Portuguese often places the subject after the verb in subordinate clauses, so assim que acabar o vídeo is very natural. Assim que o vídeo acabar is equally fine and removes any ambiguity.

How do I say “finish watching the video” explicitly?

Use a complement:

assim que acabar de ver o vídeo or assim que terminar de ver o vídeo.

Note: acabar de + infinitive in the present or perfect means “to have just done” (e.g., Acabei de ver o vídeo = “I’ve just watched the video”), so don’t confuse that with “finish doing.”

Can I start with the time clause?

Yes: Assim que acabar o vídeo, prometo devolver os auscultadores. When the time clause comes first, add a comma.

Could I say Prometo que vou/irei devolver?

Yes:

Prometo devolver… is concise and very natural.
Prometo que vou devolver… is also common.
Prometo que irei devolver… is more formal/emphatic. Avoid overusing the synthetic future if you don’t need the extra weight.

Any quick pronunciation tips (Portugal)?

prometo: pro-ME-tu (tap the r).
devolver: dih-vol-VER (very light final r).
os
- vowel links as a z sound: os auscultadores ≈ “oz…”.
assim: a-SSEENG (final nasal).
auscultadores: owsh-cool-ta-DO-rish.
vídeo: VEE-deh-oo (stress on ví).

Should there be a comma before assim que here?

Not when the time clause follows the main clause: Prometo devolver… assim que acabar… (no comma). Use a comma if the time clause comes first.

Is acabar-se ever used here?

No. acabar-se means something runs out/ends by itself (e.g., A bateria acabou-se). For finishing an activity, use acabar [algo] or acabar de/terminar de [fazer algo].