Voy a cambiarme de camiseta antes de la videollamada.

Voy a + infinitive is a very common way to talk about the near future in Spanish, especially in everyday speech.

So:

• Voy a cambiarme = I’m going to change
• A simple future would be me cambiaré

Both are possible, but voy a cambiarme sounds very natural and conversational here.

Because cambiarse means to change oneself / to get changed.

In this sentence, the speaker is changing what they are wearing, so Spanish often uses the reflexive form:

• cambiar = to change something
• cambiarse = to change clothes / get changed

Compare:

• Voy a cambiar la camiseta = I’m going to change the T-shirt
• Voy a cambiarme de camiseta = I’m going to change my shirt / change into a different T-shirt

So the me shows that the action is happening to the speaker themself.

In Spanish, when you have an infinitive, a reflexive pronoun can often go:

• attached to the infinitive, or
• before the first conjugated verb

So these are both correct:

• Voy a cambiarme de camiseta
• Me voy a cambiar de camiseta

They mean the same thing. The version in your sentence is just one very common placement.

This is a very common Spanish structure:

• cambiarse de ropa
• cambiarse de camisa
• cambiarse de camiseta

Here, cambiarse de camiseta means to change one’s shirt / to put on a different T-shirt.

This is slightly different from:

• cambiarse la camiseta

That can also be used, but it focuses more on changing the shirt itself.
With cambiarse de camiseta, the idea is very naturally to change into another shirt.

A useful way to think of it is:

• cambiarse de + clothing item = change out of one and into another

Because in this structure, Spanish often uses de + clothing item without an article when speaking generally about changing clothes.

So:

• cambiarse de camiseta
• cambiarse de ropa
• cambiarse de zapatos

This does not sound incomplete in Spanish. It is the normal idiomatic pattern.

In English we usually need something like my shirt or a shirt, but Spanish often does not.

No, they are different.

• camiseta = T-shirt
• camisa = shirt, usually a more formal button-up shirt

So in this sentence, camiseta suggests something like a T-shirt or casual top.

In Spain, camiseta is the normal word for T-shirt.

Because antes normally needs de before a noun.

So:

• antes de la videollamada = before the video call
• antes de comer = before eating

If what follows is a noun phrase, you usually need de.

Compare:

• antes de la videollamada = before the video call
• antes de que empiece la videollamada = before the video call starts

So de is required here.

Use:

• antes de + noun / infinitive
• antes de que + verb

Examples:

• antes de la videollamada = before the video call
• antes de entrar = before going in
• antes de que empiece = before it starts

A very important point: after antes de que, Spanish normally uses the subjunctive:

• antes de que empiece la videollamada

Because the speaker is referring to a specific video call that both speaker and listener can identify.

So:

• antes de la videollamada = before the video call

If it were less specific, another option might be:

• antes de una videollamada = before a video call

But in your sentence, it sounds like there is one particular call coming up.

Yes. Videollamada is commonly written as one word in modern Spanish.

It means video call.

Other similar words are also often written as one word in Spanish, for example:

• videojuego = video game
• videoconferencia = video conference

So videollamada is the standard spelling.

Because Spanish often leaves out subject pronouns when the verb already shows who the subject is.

Here:

• voy already means I go / I’m going

So yo is not necessary:

• Voy a cambiarme de camiseta... = normal
• Yo voy a cambiarme de camiseta... = possible, but more emphatic

Spanish drops subject pronouns much more often than English does.

Yes. Spanish word order is flexible.

For example, these are all natural:

• Voy a cambiarme de camiseta antes de la videollamada.
• Antes de la videollamada, voy a cambiarme de camiseta.
• Me voy a cambiar de camiseta antes de la videollamada.

They all mean basically the same thing. The differences are mainly about emphasis and rhythm, not core meaning.

In this sentence, it specifically means changing your T-shirt / top.

If you wanted to say get changed more generally, you could say:

• Voy a cambiarme = I’m going to get changed
• Voy a cambiarme de ropa = I’m going to change clothes

So de camiseta makes it more specific: the speaker is changing their shirt, not necessarily all their clothes.