Alembic
Alembic is a 3D open source exchange format developed by Lucasfilm and Sony Pictures Imageworks that is based primarily on the most common elements of 3D animated projects: Animated geometry, particles and splines.
When an Alembic file is imported, all objects in the file will be imported as special Alembic objects that each contain a link to the corresponding object in the *.abc file (this is necessary because the animation information lies in the Alembic file and NOT in Cinema 4D). If the *.abc file is modified, these changes will be assumed by Cinema 4D when the Project is reloaded or rendered. Hence, when the Project is passed on to another artist / studio / computer, etc. (or rendered with Team Render) both the *.c4d and the *.abc files must be kept together. A Cinema 4D Project can be linked to numerous Alembic files at the same time.
When the Timeslider is moved, Cinema 4D extracts the animation information from the Alembic file (which contains ,samples’ of the animation state of each frame). If Cinema 4D cannot locate the Alembic file(s), the objects will remain in the saved (non-animated) state.
Alembic is a format that is primarily designed for the loss-free transfer of animated geometry to other applications. This format has been highly optimized for this purpose and offers much smaller file sizes than for example *.obj. The Alembic format can also be advantageous within the actual Cinema 4D workflow. Memory use can be lowered dramatically if complex animations (incl. Dynamics) are saved using the Alembic format and subsequently loaded into Cinema 4D since the complete animation information does not have to be cached. In addition, low-res dummy objects can be used for editing that can be replaced by high-res objects for rendering (see Alembic object).
It is also possible to use Alembic to load highly complex animations that would otherwise force Cinema 4D into submission. If, for example, you want to bake Thinking Particles (or other "difficult to fixate" elements), these can be stored in an Alembic file and subsequently integrated into the Project.
In addition to the Alembic-specific settings, several Alembic objects (which are actually Generators) have additional modifiable settings (e.g., the Phong tag for polygonal objects or the Subdivision Surfaces tab for Subdivision Surface objects) in the Attribute Manager (Object tab). Depending what the Alembic file specifies, certain parameters can be locked. Alembic objects can be converted to real Cinema 4D objects by pressing the C. Of course these can then no longer be linked to an Alembic file.
Bake Objects... to modify an Alembic object you can create a copy of this object with the animation track contained in the Alembic file, including keyframes.