Difference between meditating and watching a movie If I meditate, I concentrate on my breathing; if my mind wanders, I bring its attention back to my breathing.

If I watch a movie/show, I concentrate on it; if my mind wanders, I bring its attention back to the movie/show.

So what's the difference? (other than one is more entertaining than the other)
You are comparing two totaly different things.

While watching a movie/show, you let allday grind behind you and consume the input you get.
This can have several effects on your consciousness, both temporal and permanent, just like meditation. 
But these two points are everything what meditation and watching a movie/show are having in common.

Everyone knows what watching a movie/show is due everyone has expirience in it, so I will not go further to this point.
But I assume that you do not anderstand the point of meditation.
It's not only about watching your breath and prevent your thoughs of wandering around.
Für meditation-beginners this might be true, due they first have to lern to focus.

But meditation is a lot more. Depending on what a person wants to archive by meditation.
Essentially one focus his mind on either the body, the mind itself(like in a mirror) or both at the same time. 

One can write a lot of books about what you can archive due meditation, so I avoid to write a long text.

Most people do not explore their mind. They see it as a kind of invisible organ which is just there and has a function.
But as many people do sport to train their body, other people meditate to train their mind.
Not only to focus their thoughs on one spot, but also to conditionate their thoughts, overcome traumatic memory or just to archive highest cognitive capacity without using drugs. 

Due meditation, one discovers his own mind. This will take years and the exploration will never ends, due the mind changes his state with the years.
By meditation one watches the mind changing, finds his own  weakpoints, learns on wich kind of input it reacts in wich way and to avoid "bad" input and search "good" input.

Typical results of years of meditations can be:
- Acceptance to things that stressed the mind in the past.
- Or exactly the opposite: rais of the courage to change something one suffered for a while.
- More happyness due the "I really controll myself" state, like a athlete.

In the end I tell you:
If you want to know what meditation is about, you have to try it out.
If you are willing to do, I recommend you to start the "focus on breath" technique to learn the focus, but keep in mind that this is just a small step. The aim is to focus the mind.

If you want more information, sent me a message.