To talk about

To talk about
 

I would say hablar sobre as in Vamos a hablar sobre el cambio de....

I saw written, hablar tras instead of hablar sobre. Is tras a preferred usage?

Thanks

"Hablar tras (algo)" is not talking about a subject, but to talk after an event has happened; the talk is certainly related to the event, but not necessarily all about it.

- El futbolista habló tras salir del hospital. -> He was in hospital and spoke to the press after he left. His talk must have been related with the reasons why he went to the hospital, how long he stayed and his future as a football player, but it was not necessarily focused on his leaving the hospital as only topic.
- El Presidente habló tras la muerte del famoso escritor. -> He spoke after the writer died.
- Nuestra representante habló tras el desacuerdo con la empresa. -> She spoke after there was a disagreement.


...And "hablar tras (alguien)" means that someone talks after someone else:

- El director de la escuela habló tras el jefe de los padres de familia. -> The head of the parents association spoke first, then the school principal.
- La alcaldesa habló tras el líder obrero. -> She spoke after the worker union leader.