Which type of track in the timeline cannot be added without additional coding?

The type of track in Unity's Timeline that cannot be added without additional coding is the Light Control Track. This is because the Light Control Track requires custom functionality for it to properly manipulate the lighting settings in the scene. Unity provides various built-in tracks, including Animation and Sound Tracks, which are readily available and can be used directly in the Timeline without any additional code.

In the case of the Light Control Track, creating custom light behaviors typically necessitates scripting to define how the lighting should change over time. This means that developers must implement specific code to manipulate light properties such as intensity, color, or even enable/disable a light, thus requiring additional steps beyond merely adding the track to the Timeline.

In contrast, Animation Tracks and Sound Tracks are straightforward to use as they allow for the direct application of animations and audio clips that are already integrated within Unity’s framework, making them available out of the box. The Animation Control Track similarly functions within the established systems of the animation workflow in Unity without the need for additional custom scripts.