Comprimo il video: riduco la dimensione senza cambiare la risoluzione.

Comprimo is the 1st person singular present tense of comprimere: I compress.

• io comprimo = I compress
• lui/lei comprime = he/she compresses

So in Comprimo il video, the speaker is saying I compress the video.

Compressa would not work here because that is not a present-tense verb form in this sentence. It can be a past participle/adjective in other contexts, but not the form you need here.

The infinitive is comprimere, which means to compress.

This is a -ere verb, but it is not completely regular in all forms, so it is worth learning the present tense pattern:

• io comprimo
• tu comprimi
• lui/lei comprime
• noi comprimiamo
• voi comprimete
• loro comprimono

A learner may expect something simpler, but comprimo is the correct form.

Italian often omits subject pronouns when they are not needed.

So:

• Comprimo il video = I compress the video
• Io comprimo il video = also correct, but more emphatic

Because the verb form comprimo already tells you the subject is I, Italian usually leaves out io unless the speaker wants contrast or emphasis.

For example:

• Io comprimo il video, tu comprimi l’audio.
  = I compress the video, you compress the audio.

In Italian, the definite article is used more often than in English.

So il video literally means the video, but depending on context it may correspond to English the video or just video.

Here, il is the masculine singular article used before video.

• il video
• il file
• il documento

Even when English might sound natural without an article in some technical language, Italian often keeps it.

Here, video is singular: the video.

The interesting thing is that video often has the same form in singular and plural in modern Italian:

• il video = the video
• i video = the videos

So the article tells you the number:

• il = singular
• i = plural

Riduco is the 1st person singular present tense of ridurre, meaning to reduce.

So:

• riduco la dimensione = I reduce the size

Like comprimere, ridurre is not a perfectly regular verb, so it is good to learn its forms rather than guessing from the infinitive.

Some present-tense forms are:

• io riduco
• tu riduci
• lui/lei riduce
• noi riduciamo
• voi riducete
• loro riducono

La dimensione is singular and means the size.

In English, dimensions often refers to width, height, depth, etc., but in this sentence the meaning is more like file size or overall size, so Italian naturally uses the singular dimensione.

So:

• riduco la dimensione = I reduce the size

If you said le dimensioni, that would more naturally suggest the dimensions in the sense of measurements.

After senza in Italian, you normally use the infinitive when the subject stays the same.

So:

• senza cambiare la risoluzione = without changing the resolution

This is the standard structure:

• senza + infinitive

Examples:

• senza parlare = without speaking
• senza perdere tempo = without wasting time
• senza modificare il file = without modifying the file

Senza cambiando is not correct here.
Senza cambio would also be wrong, because cambio is not the right verb form for this structure.

Italian usually includes the article in this kind of phrase, so la risoluzione is the natural form.

• cambiare la risoluzione = to change the resolution

In technical or headline-like language, articles are sometimes omitted, but in a normal full sentence the article sounds more natural.

The colon introduces an explanation or clarification.

So the structure is:

• Comprimo il video:
  general statement
• riduco la dimensione senza cambiare la risoluzione.
  explanation of what that means

In English, it works similarly:

• I compress the video: I reduce the size without changing the resolution.

It is showing that the second part explains the first part.

Italian often uses the present tense to describe:

1. what someone is doing now, or
2. a general process or habitual action

So this sentence can mean something like:

• I’m compressing the video
• When I compress a video, I reduce the size without changing the resolution
• I compress the video by reducing its size without changing the resolution

The exact interpretation depends on context. Italian present tense is flexible, just like English present can be in some contexts.

Yes. They are related, but not identical.

• comprimere il video = to compress the video
• ridurre la dimensione = to reduce the size

The sentence uses both because the second part explains the first:

• Compressing the video means
• reducing its size without changing the resolution

So comprimere is the overall action, while ridurre describes the effect.

A simple pronunciation guide:

• comprimo → kom-PREE-mo
• dimensione → dee-men-syo-NEH
• risoluzione → ree-zo-loo-TSYO-NEH

A few helpful points:

• Italian stress often falls near the end in words like dimensione and risoluzione
• z in risoluzione sounds like ts
• zione is commonly pronounced like tsyoh-neh

If you want to sound natural, keep the vowels clear and pure, without turning them into diphthongs as English sometimes does.

Yes, but it changes the nuance.

• Comprimo il video = I compress the video / I’m compressing the video
• Sto comprimendo il video = I am in the middle of compressing the video right now

The stare + gerundio form emphasizes an action in progress.

So if you want to describe the process happening at this moment, sto comprimendo il video is very natural.
If you want a more general or neutral statement, comprimo il video works well.

Yes, it is natural and clear, especially in a technical or explanatory context.

It sounds like someone is explaining what video compression does. The wording is straightforward and standard:

• Comprimo il video = action
• riduco la dimensione senza cambiare la risoluzione = explanation

If you wanted an even more technical phrasing, you might also hear things like:

• Comprimo il video per ridurne la dimensione senza modificarne la risoluzione.

But the original sentence is perfectly good and easier for a learner to understand.