jadongcha beullaekbakseuga jungyohan jeunggeoga dwaesseoyo.

In everyday Korean, 블랙박스 usually means a car dashcam or dashcam footage, not an airplane flight recorder.

So in this sentence, 자동차 블랙박스 most naturally refers to the car’s dashcam.

Korean uses this loanword very commonly, and its real-life meaning is a bit narrower than the English black box.

Korean often puts nouns together to make a compound noun phrase.

So:

• 자동차 = car
• 블랙박스 = dashcam / black box
• 자동차 블랙박스 = car dashcam

This is similar to how English can stack nouns in phrases like car door or coffee cup.

Korean often does this without 의, so 자동차 블랙박스 sounds natural. You could also say 자동차의 블랙박스, but that sounds a little more explicitly like the car’s dashcam.

This is a very common pattern in Korean.

The structure is:

X가 Y가 되다 = X becomes Y

So here:

• 자동차 블랙박스가 = the car dashcam
• 중요한 증거가 되다 = to become important evidence

The first 가 marks what is being talked about as the subject. The second 가 marks what it became.

So the sentence is built like:

The car dashcam + became important evidence

This double-가 structure is normal with 되다.

Because 중요하다 is a descriptive verb (an adjective-like word in Korean), not an action verb.

When a descriptive verb modifies a noun, it usually takes -ㄴ/은:

• 중요하다 → 중요한
• 예쁘다 → 예쁜
• 크다 → 큰

So:

• 중요한 증거 = important evidence

By contrast, action verbs use -는:

• 공부하다 → 공부하는 학생 = a student who studies

So 중요하는 would be incorrect here.

증거가 되다 literally means to become evidence, but in natural English it often means something like:

• to serve as evidence
• to turn out to be evidence
• to end up being important evidence

So this sentence does not necessarily mean the dashcam physically changed into evidence. It means that, in the situation being discussed, it came to function as important evidence.

Yes. 됐어요 is the past polite form of 되다.

The full form is:

• 되었어요

But in normal speech and writing, this is usually contracted to:

• 됐어요

So:

• 되다 = to become
• 되었어요 / 됐어요 = became

Both are correct, but 됐어요 is much more common in everyday Korean.

Using 가 makes the sentence feel like a neutral statement about what became important evidence.

• 블랙박스가 중요한 증거가 됐어요
  = The dashcam became important evidence.

If you used 는 instead:

• 블랙박스는 중요한 증거가 됐어요

it would sound more like:

• As for the dashcam, it became important evidence
• or it could suggest contrast, such as the dashcam, at least, became important evidence

So 가 is the more natural default choice here unless you specifically want topic or contrast.

Yes, you could.

The difference is mainly in style and nuance:

• 자동차 블랙박스가 = a natural compound expression, very common
• 자동차의 블랙박스가 = more explicitly the car’s dashcam

In many everyday Korean phrases, 의 is omitted when the relationship is obvious. That is why 자동차 블랙박스 sounds perfectly natural.

It is pronounced roughly like 돼써요.

That is because:

• 되었어요 contracts to 됐어요
• in pronunciation, 됐 sounds close to 됃/돼ㅆ

So when listening, you will usually hear something close to 돼써요, not a careful syllable-by-syllable 되-었-어-요.

This is a very common spoken form, so it is good to get used to hearing it.