In Homeworld 1 Remastered, missions are separated by cut-scenes. These cut-scenes only play in between missions, and are distinct from the in-game videos which can appear during a mission. If you see a pre-rendered cut-scene, you know you’re headed to the next mission.
If you have difficulty with missions or other aspects of the game, drop us a line at http://support.gearboxsoftware.com.