The word filmaban is the imperfect form of filmar in the third person plural.
See the full filmar conjugation

filmar

El escenario donde se filmaban era importante.
The setting of where they happen is very important.
Una vez, yo interpretaba la escena y me filmaban a mí.
One time, I was playing the scene and the camera was on me.
Lo arrestaron a él y a los que filmaban.
And they arrested the driver and they arrested people who were filming.
De todos modos, no los filmaban mucho.
Not that they were filmed much anyway.
Recuerdo como filmaban a la gente.
I remember that once they filmed people.
Filmaban todo el tiempo.
They filmed all the time.
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