Complex sentence: Morrison's description has been dubbed onto the newsreel film of the crash, giving the impression of a modern television-style broadcast, but at the time newsreels were separately narrated in a studio and Morrison's words were not heard in theaters.
Split into simpler sentences: Morrison's description has been dubbed onto the newsreel film of the crash, giving the impression of a modern television-style broadcast. However, at the time, newsreels were separately narrated in a studio and Morrison's words were not heard in theaters.