Canon EOS 5D MARK IV Instruction Manual page 339

ISO Speed in the <A> Mode
L: Full HD movie/w: High frame rate movie shooting
The ISO speed will be set automatically within ISO 100 - ISO 25600.
H: 4K movie shooting
The ISO speed will be set automatically within ISO 100 - ISO
12800.
ISO Speed in the <d>, <s>, <f>, and <
L: Full HD movie/w: High frame rate movie shooting
The ISO speed will be set automatically within ISO 100 - ISO 25600.
In [Range for movies] under [z2: ISO speed settings], if you set
[Maximum] to [H2 (102400)] (p.379), the maximum limit of the
automatic ISO speed setting range will be expanded to H2
(equivalent to ISO 102400). Note that even if you set the [Maximum]
and [Minimum] to a narrower range than the default ISO range (ISO
100 - ISO 25600), it will not take effect.
If [z3: Highlight tone priority] is set to [Enable] (p.206), the
automatic ISO speed setting range will be ISO 200 - ISO 25600.
H: 4K movie shooting
The ISO speed will be set automatically within ISO 100 - ISO 12800.
Under [z2: ISO speed settings], if you set [Range for H]'s
[Maximum] setting to [H2 (102400)] (p.379), the maximum limit of
the automatic ISO speed setting range will be expanded to H2
(equivalent to ISO 102400). Note that even if you set the [Maximum]
and [Minimum] to a narrower range than the default ISO range (ISO
100 - ISO 12800), it will not take effect.
If [z3: Highlight tone priority] is set to [Enable] (p.206), the
automatic ISO speed setting range will be ISO 200 - ISO 12800.
For movie shooting, the ISO speed cannot be expanded to L (equivalent
to ISO 50).
When switching from still photo shooting to movie shooting, check the
ISO speed settings again before shooting movies.
k Shooting Movies
> Modes
F
337