My first example of music composed for a game is from Bioware's "Mass Effect" which is a Role-Playing game for the PC and Xbox 360. The game is based in futuristic, space environments, and the music greatly accentuates this feel and establishes a brilliant atmosphere. As mentioned earlier, music in video games must be be composed in a way that can be played over an undetermined length of time.
Notice the simple structure of the songs in these two clips (notably the background music of the map screen in the beginning of the first clip). They follow a very simple 4/4 structure and keep a similar tone continuously, rather than beginning with a build up or something that a regular song may contain. This creates ease when creating a seamless loop in the music.
If the music in an area is ever calm, it will blend into a more appropriate score when the player is faced with combat. Listen to the music in this next clip and notice the louder and more dramatic score whist the player is in battle, as opposed to the more subtle and ambient music in the examples I provided earlier.
My next example is from Konami's "Metal Gear Solid 4" for the Playstation 3. The Metal Gear Solid series is a widely renowned game and is very well established as being extremely similar to a film, with the fourth instalment containing cutscenes of up to 90 minutes. The following clip is taken from the end of the game and displays the main protagonist in an extremely tense situation of walking through a microwaved hall.
As you'll notice, it is split into two sections throughout this segment of the game and plays out like an interactive cutscene with you controlling the bottom half, whilst the top half shows what is happening outside of the hallway. The music is extremely dramatic and is very similar to that of a movie score. This can actually be done here due to the timed nature of the gameplay in this particular section of the game. If the character doesn't get through the hallway in a specific amount of time (after which the song would end) then he will die and the chapter will start again.
The next clip is from the very end of the game and utilises an extremely brilliant use of music. It should be noted that Metal Gear Solid 4 is the final game in the series, and during the lengthy final battle, the main themes of the previous three games are played chronologically in the background.
The reason I find the use of all the main themes from the previous games is because I am a huge fan of the series, and the themes are instantly recognisable to me and other fans of the games. Implementing this at the very end of the final game is also like a retrospective on the past 10 years of the series' existence and creates a feeling of nostalgia for the player.
Another game with excellent use of music is United Game Artist's "Rez". The entire game is built around music and rhythm whilst combining exceptionally elaborate visuals. The game is notable for replacing the typical sound effects found in most rail shooter games with electronic, using sounds and visuals when the player destroys a target.
My fourth and final example is from Harmonix's "Rock Band". Rock Band is a rhythm based game soley focusing on using instrument controllers to play the notes or sing in tune with what is being shown on screen.
The top lane is the vocal track, the left lane is the guitar track, the middle lane is the drum track and the right lane is the bass track. All of the notes coming down the track need to be played using the specially dedicated controllers in order to play the song. If the player misses then the song will cut out for a short period of time. This is an extremely popular franchise and shows the use of music in video games in an extremely different light.