Sibcam files store per-frame camera transformations for cutscene direction. This includes position, rotation, scale and their respective differences from the previous frame. Additionally the FoV can be changed between desired frames.
There is simple compression for values that have already appeared in previous frames, but it's optional. Frames can apparantly also be outright skipped, leaving gaps in the numbering of frames.
This camera animation mustn't be longer than the cutscene animation, otherwise the game will crash.
These files can be found in the cutxxx/ folders of every .remobnd archive, which themselves are stored in the remo/ folder
SibcamBuilder - a simple commandline tool to convert .damnhavok files to sibcam files