He was in the middle of shooting a documentary about Prague Spring for a US producer when the Warsaw Pact invasion happened. He smuggled his footage of invasion to Vienna, where it was broadcast on Austrian television. He edited the footage together with the Prague Spring documentary and released the film as "Oratorio for Prague". It received standing ovations in New York Film Festival in the fall of 1968. Němec's footage would eventually be used by countless international news organizations as stock footage of the invasion. Philip Kaufman's film adaptation of "The Unbearable Lightness of Being" (1988) used footage from the film; Němec also served as an advisor.