When you're shooting video, the way you control the exposure parameters is a bit different than when you're shooting photos. This helpful video will teach you one of the things to consider when choosing the correct ISO for video.
Coming to you from wolfcrow, this great video will introduce you to the concept of native ISOs. If you've not heard of native ISO before, it's the natural ISO of your sensor. Every digital sensor has only one (or two in the case of a dual native ISO sensor) actual ISO sensitivity; when you change the ISO setting, you're actually applying a gain to the signal, not changing the sensitivity of the sensor itself. Dual native ISO cameras are relatively rare; the most common consumer-level device is probably the Panasonic GH5S, which has native ISOs of 400 and 2,500. When it comes to still photos, you often might not care that much if your ISO varies from shot to shot, so long as it was the appropriate level for each specific image. On the other hand, when it comes to video, when you bring each individual shot onto your timeline, you want to maintain a consistent look as you move from shot to shot to lend the finished product a good level of cohesiveness, and the noise level jumping around constantly will undermine your efforts to do so. Check out the video above for some good advice on how to tackle that problem.