Composing interactive music for Games

Games are not inherently a storytelling medium.
At least not in a sense that books or movies are storytelling Mediums. Although games often have a story between the gameplay (where the real game is happening), it is seldom intertwined within the gameplay (which is a pity). Most of the games we have are disconnected from the story. That's why you can watch just the cutscenes of the game and basically have a movie, where all the major plotpoints happen. There are of course exceptions to that, and those games can be scored much more easily.

So what is the story in a game?
In super mario, the story is not that mario has to defeat bowser in order to rescue the princess. The real story, the drama, is within the gameplay.
And games tell stories pretty similar to music actually.
First, there is an idea. A mechanic. Like jumping above pits. Something which is inherently interesting.
Then there is the development of the idea. The idea gets explored from different perspectives. What else can we do with it? What if we make the player jump not above a pot which is one block wide, but instead two blocks wide and is a bit lower? Or higher. What if there are enemies who can kill him in the way…
And finally there is the recapitulation. A final challenge for the player, who, if he came this far, is now a master in jumping over pits. This is not necessarily the hardest challenge. This one is fun. A run through the finish line. A celebration. The end boss of a level is, for pacing reasons, never the hardest challenge.
This is the typical ABA structure, while the last A is bigger, louder and more complete.

So how do we do this?
Games are not always linear and just in rare cases deterministic like music. Cutscenes of course will be scored like we score movies. But the gameplay?

I have picked three examples of how a level is scored in different games, which are quite similar.
Those three genres are pretty much the same in terms of its gameplay design, so pretty interesting to observe how the problems of dynamic music is solved here in an action sequence:

Tomb raider

Uncharted

Indiana Jones

If you ask me, I much prefer the approach of the Indiana Jones game. The music dictates the action here, not the other way around, which makes sense, since it is an arena where the player has no other option than fighting. Even though the player starts hiding at the beginning, the music tells him, that it is time for a battle to proceed.
the first to examples are the result of over complicating. The music tries to match every step of the player, but instead it should match to the drama the game wants to create! They have no other choice to than to do generic, unmusical drum loops in order to be able to adjust to whatever the player wants to do, like hiding during a gun fight.

So, our goal is to not just do unmusical drum loops and layer in new instruments. We want to do horizontal development instead of vertical development. We want to tell the drama of the gameplay.
The easiest and most efficient way is to do loops for each of these sections and transition between them with Stingers. Or stingers leading into a transition section to the new loop. But remember to play the drama of the gameplay!
Here is a great example how to do this:

you can skip to 35:13, but I recommend the full talk. As you can see there is not even battle music, when the player is fighting in these examples. That is because the drama is exploring, not fighting in those cases.

There have been attempts to make better, more musical transitions between loops. LucasArts did this with a system called iMuse. The composers defined hook points in each loop, and composed a transition or ending from each defined point. You can view them in action here:

However, the players and the press never noticed. So in the end it was way too much effort to compose these transitions when players were fine with just stopping and starting loops. This may be because of the genre of point and click adventures, since people are used to music suddenly starting and stopping when they click with their mouse, or because they were accustomed to those hard transitions in these games. But it would be really conspicuous if we would not do transitions at all nowadays.
There is software like FMOD among others, which are often used in games nowadays. It enables you to do vertical sequencing, as well as horizontal transitions. But be careful which way you go down for each scene or level. As Gareth Coker said in his GDC talk: You have to playtest your music within the game to find the best approach.

Now, there are also games which need some environmental music. Like music for a specific place, which is always played when you visit it. There is hardly a story to tell now is it? Well, depending at which point of the overarching story the player currently is, this music can be different. You can use your themes here and make this place feel a bit different after the player got to act 2.
Or you compose those places like loops in amusement parks. Hitting a certain vibe and doing a variation of one of your themes maybe. Or do a new theme for this place if it contributes to the overarching story.

I hope this is of help for anyone. Feel free to discuss and state your ideas how to best approach game music.