"MPEG-4 part 2 (DivX/Xvid, etc.)" - did you mean "MPEG-2 part 4 (DivX/Xvid)", hence the (misleading) filename extension "mp4"?
mp4 the media container is https://en.wikipedia.org/wiki/MPEG-4_Part_14
MPEG-2 part 4 is some conformance testing specification.