Shooting Movies - Canon EOS-1D X Instruction Manual

The live image displayed on the camera's LCD monitor
can be recorded as a movie to the card. The movie
recording format will be MOV.
Cards that Can Record Movies
When shooting movies, use a large-capacity card with a
fast writing/reading speed as shown in the table.
Compression Method
(p.239)
If you use a slow-writing card when shooting movies, the movie
may not be recorded properly. Also, if you play back a movie on
a card with a slow reading speed, the movie may not play back
properly.
If you want to shoot still photos while shooting a movie, you will
need an even faster card.
To check the card's reading/writing speed, refer to the card
manufacturer's website.

Shooting Movies

IPB
ALL-I (I-only) 30 MB/sec. or faster
7
10 MB/sec. or faster
225