Мы смонтировали короткометражку.

Смонтировали is the past tense plural form of смонтировать.

Breakdown:

• с- = prefix
• монтировать = to edit / assemble / mount
• смонтировать = perfective verb, meaning to finish editing / assemble completely
• -ли = past plural ending

Because the subject is мы (we), the verb takes the plural past form: смонтировали = we edited / we put together / we finished editing.

In Russian past tense, plural forms do not show gender. Only singular past forms do:

• я смонтировал = I did (masculine speaker)
• я смонтировала = I did (feminine speaker)
• мы смонтировали = we did

Russian uses aspect, and this sentence uses the perfective verb смонтировать because it presents the action as completed.

So:

• мы монтировали короткометражку = we were editing / we edited a short film (focus on process, duration, or repeated activity)
• мы смонтировали короткометражку = we finished editing the short film (focus on result)

A native English speaker often misses this nuance because English does not mark aspect in the same way with separate verb pairs.

Here, perfective fits because the sentence is about a completed outcome: the short film is now edited.

Here смонтировать means something like:

• to edit
• to assemble
• to put together

In the context of film, it usually means to edit the footage into a finished film.

Be careful: in other contexts, смонтировать can also mean to install or to assemble physically.

For example:

• смонтировать видео = to edit a video
• смонтировать оборудование = to install/assemble equipment

So the exact English translation depends on context.

Because it is in the accusative singular.

The base form is:

• короткометражка = a short film / short movie

This is a feminine noun ending in -а, so in the singular accusative it changes:

• nominative: короткометражка
• accusative: короткометражку

It is accusative because it is the direct object of the verb:

• Мы смонтировали что?
  Короткометражку.

That is one of the most common patterns in Russian:

• книга → книгу
• машина → машину
• короткометражка → короткометражку

Короткометражка is a common, fairly informal or neutral everyday word meaning short film.

It comes from короткометражный фильм:

• короткометражный = short-featured / short-length
• фильм = film

So:

• короткометражный фильм = short film
• короткометражка = a shortened everyday version

This kind of shortening is very common in Russian. A learner should recognize that короткометражка is natural speech, not strange slang.

It could absolutely be omitted.

Russian often leaves out subject pronouns when they are clear from the verb form. Since смонтировали already shows plural past, the sentence can be:

• Смонтировали короткометражку.

That can still mean We edited the short film, depending on context.

Including мы adds one of these effects:

• extra clarity
• extra emphasis on we
• contrast, as in We edited it, not someone else

So both are possible:

• Мы смонтировали короткометражку.
• Смонтировали короткометражку.

Yes, Russian word order is flexible.

The neutral order here is:

• Мы смонтировали короткометражку.
• literally: We edited a short film.

But you can change the order for emphasis:

• Короткометражку мы смонтировали. = It was the short film that we edited.
• Смонтировали мы короткометражку. = marked, contrastive, less neutral

Even though word order can change, the case endings still show the grammatical roles:

• мы = subject
• короткометражку = direct object

So Russian relies less on word order than English does.

Russian has no articles.

So короткометражку can mean:

• a short film
• the short film

The exact meaning depends on context.

For example:

• if this is new information, it may feel like a short film
• if both speakers already know which film, it may feel like the short film

English forces you to choose; Russian usually does not.

You would usually use the imperfective verb:

• Мы монтировали короткометражку.

That can mean:

• We were editing a short film
• We edited a short film (with focus on the activity, not the completed result)

Compare:

• Мы монтировали короткометражку весь вечер.
  We were editing the short film all evening.

• Мы смонтировали короткометражку за два дня.
  We edited/finished the short film in two days.

A useful rule:

• imperfective = process, duration, repetition
• perfective = completion, result, one whole finished action

Yes. A more formal or explicit version would be:

• Мы смонтировали короткометражный фильм.

That means the same thing, but sounds more formal and less conversational than короткометражку.

So:

• короткометражка = everyday, compact, natural in speech
• короткометражный фильм = full form, more formal or descriptive

Both are correct.

The stress is:

• смонтИровали

So the stressed syllable is ТИ.

And:

• короткометрАжку has stress on РАЖ

Stress matters in Russian, so it is worth learning words together with their stress:

• смонтИровать
• смонтИровали
• короткометрАжка
• короткометрАжку

Yes, in a literal sense смонтировать has the idea of putting something together, so assembled is not wrong as a core idea. But in film context, the most natural English translation is usually:

• We edited a short film
• We cut a short film
• We put together a short film

So for a learner, the safest understanding here is film editing, not physically building something.