Complex sentence: On July 23,2016, a teaser production trailer was released by HBO at 2016 San Diego Comic-Con, the trailer mostly contained voice overs, and shots of crew members creating sets and props.
Split into simpler sentences: On July 23,2016, a teaser production trailer was released by HBO at the 2016 San Diego Comic-Con. The trailer mostly consisted of voice overs, and shots of crew members creating sets and props.