Opening Sequences

The opening credits are present at the beginning of most movies in text form to acknowledge and credit the most important people in the production of that particular film for example the actors, the editor or even the writer whereas the title sequence is the action used to give the viewers an idea of where the film is set or who the characters are so that they have a little idea of what to expect during the film. 

In an opening sequence you can have conventions such as non-diegetic sounds such as a soundtrack to create an atmosphere, graphic matches can also be an effective technique in a title sequence. Some editors may choose to make the opening sequence quite abstract so that it doesn't give too much away it may just give you a clue as to where it's set or the genre of the movie. Some movies start off with a Cold Opening which is when a little bit of action or dialogue within the movie begins to take place before they show the opening sequence. Some opening sequences are entirely animated whereas some are based on real characters and real settings which also helps determine the genre. A narrator can also be used to set the scene.