Der Ton im Video ist leise, aber das Bild ist klar.

Because German nouns have grammatical gender, and you have to learn each noun with its article:

• der Ton = masculine
• das Bild = neuter
• das Video = neuter

The gender does not always match English logic, so it usually has to be memorized with the noun.

im is a contraction of in dem.

• in dem Video → im Video

So im Video means in the video.

This is very common in German:

• am = an dem
• im = in dem
• zum = zu dem

Here, in describes a location: the sound is quiet in the video. For location, German uses dative with in.

So:

• in dem Video / im Video = in the video (location, dative)

If you were talking about movement into something, you would use the accusative:

• in das Video = into the video

This is because in is a two-way preposition: it can take either dative or accusative depending on meaning.

Because in this sentence they are predicate adjectives. They come after the verb sein and describe the subject.

• Der Ton ist leise.
• Das Bild ist klar.

After sein, adjectives usually do not take endings.

Compare:

• der leise Ton = the quiet sound
  here leise comes before the noun, so it gets an ending

• Der Ton ist leise.
  here leise comes after ist, so there is no ending

The same applies to klar.

German main clauses usually follow the verb-second rule (V2). That means the conjugated verb comes in the second position.

• Der Ton | ist | leise
• das Bild | ist | klar

Even after aber, the next clause is still a normal main clause, so the verb stays second:

• ..., aber das Bild ist klar.

No. aber is a coordinating conjunction, so it joins two main clauses without changing normal word order.

That is why you get:

• Der Ton im Video ist leise, aber das Bild ist klar.

Compare that with a subordinating conjunction like weil, which would send the verb to the end:

• ..., weil das Bild klar ist.

So:

• aber → normal main-clause order
• weil → verb goes to the end

Because aber joins two full clauses here:

• Der Ton im Video ist leise
• das Bild ist klar

In standard German, a comma is normally used before conjunctions like aber when they connect full clauses.

In this sentence, der Ton means the audio or sound of the video.

Depending on context, Ton can also mean:

• a tone
• a musical note
• the way someone speaks / tone of voice

But with im Video, it very naturally means the sound/audio.

Usually both can work in English, depending on context.

Here leise means:

• quiet
• low in volume
• too soft to hear well (depending on context)

Opposites include:

• laut = loud
• zu leise = too quiet / too soft

So Der Ton ist leise is a natural way to say the audio is quiet.

Here klar means clear in the visual sense: the picture is clear, sharp, easy to see.

With Bild, klar suggests the image is not blurry or confusing.

Related words:

• unscharf = blurry / out of focus
• deutlich = clear / distinct
• verschwommen = blurred

So Das Bild ist klar means the picture quality is clear.

Because all nouns are capitalized in German.

So in this sentence:

• Ton
• Video
• Bild

are capitalized because they are nouns.

This is one of the most noticeable spelling differences between German and English.

Grammatically, German allows many adjective-noun combinations, but not all of them sound natural.

• Der Ton ist klar can work, but then klar refers to the sound being clear, distinct, easy to hear.
• Das Bild ist leise does not make sense, because leise describes sound, not images.

So in the given sentence:

• leise matches Ton
• klar matches Bild

Yes. It is very natural and common.

It follows a simple pattern:

• [subject] + [location] + ist + [adjective], aber [subject] + ist + [adjective]

You can build many similar sentences:

• Der Kaffee ist heiß, aber das Wasser ist kalt.
• Das Zimmer ist klein, aber der Balkon ist schön.

So this sentence is a very useful model for everyday German.