Canon EOS Rebel T4i 18-135mm IS STM Lens Kit Instruction Manual page 174

k Shooting Movies
ISO speed during manual-exposure shooting
With [Auto], the ISO speed will be set automatically within ISO 100 -
6400.
You can set the ISO speed manually within ISO 100 - 6400 in whole-
stop increments. Under [54: Custom Functions (C.Fn)], if [2: ISO
expansion] is set to [1: On], the manual setting range will expand so
you can also select H (equivalent to ISO 12800).
Under [54: Custom Functions (C.Fn)], if [3: Highlight tone
priority] is set to [1: Enable], the ISO speed will be ISO 200 - 6400.
Since shooting a movie at ISO 12800 may result in much noise, it is
designated as an expanded ISO speed (displayed as "H").
Under [54: Custom Functions (C.Fn)], if [2: ISO expansion] is set to
[1: On] and you switch from still photo shooting to movie shooting, the
manual setting range's maximum will be H (equivalent to ISO 12800).
Even if you switch back to still photo shooting, the ISO speed will not
revert to the original setting.
Exposure compensation cannot be set.
Changing the shutter speed or aperture during movie shooting is not
recommended since the changes in the exposure will be recorded.
If you change the shutter speed while shooting under fluorescent or LED
lighting, image flicker may be recorded.
When ISO Auto is set, you can press the <A> button to lock the ISO
speed.
After recomposing the picture, you can see the exposure level difference
on the exposure level indicator (p.175) compared to when you pressed
the <A> button.
By pressing the <B> button, you can display the histogram.
When shooting a movie of a moving subject, a shutter speed of 1/30 sec.
to 1/125 sec. is recommended. The faster the shutter speed, the less
smooth the subject's movement will look.
174
Focus and shoot the movie.
5
The procedure is the same as steps 3
and 4 for "Autoexposure Shooting"
(p.170).