Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 320)

3 Setting the Movie Recording Quality
320
Movie Files Exceeding 4 GB
Even if you shoot a movie exceeding 4 GB, you can keep shooting
without interruption.
Using CF cards up to 128 GB formatted with the camera
If you use the camera to format a CF card with 128 GB or less in
capacity, the camera will format it in FAT32.
With a FAT32-formatted CF card, if you shoot a movie and the file
size exceeds 4 GB, a new movie file will be created automatically.
When you play back the movie, you will have to play each movie file
individually. Movie files cannot be played back automatically in
consecutive order. After the movie playback ends, select the next
movie and play it back.
Using CF cards exceeding 128 GB and CFast cards formatted
with the camera
If you use the camera to format a CF card with more than 128 GB in
capacity, the camera will format it in exFAT.
When using an exFAT-formatted card, even if the file size exceeds 4
GB during movie shooting, the movie will be saved as a single file
(rather than being split into multiple files).