Canon EOS REBEL T7i Instruction Manual page 266

k Shooting Movies
ISO Speed in Basic Zone Modes
The ISO speed will be set automatically within ISO 100 - ISO 12800.

ISO Speed in the <d>, <s>, and <f> Modes
The ISO speed will be set automatically within ISO 100 - ISO 12800.

The maximum limit varies depending on the [kISO Auto] setting
(p.308).
Under [54: Custom Functions(C.Fn)], if [2: ISO expansion] is set

to [1:On], [Max.:H(25600)] can also be selected for [kISO Auto].
Under [54: Custom Functions(C.Fn)], if [4: Highlight tone

priority] is set to [1:Enable], the ISO speed will be ISO 200 - ISO
12800.
When switching from still photo shooting to movie shooting, check the ISO
speed settings again before shooting movies.
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