CameraOnim is a Blender add-on for importing and exporting Camera ONIM files. This format is used in OpenIV for Grand Theft Auto IV.
Installation: Open Blender, go to Edit -> Preferences -> Add-ons and click 'Install...'. Select CameraOnim archive. Find it in the list of add-ons and activate it.
Usage: If you are going to make a camera animation, create a Camera object. After you have done your operations on the object, select the object and export it. To import or export the file, go to File -> Import/Export -> Camera ONIM (.onim).
Keep in mind that the frame rate of the scene affects the export. The game uses 30 FPS in cutscenes.