I'm a video novice, so I may repeat some of this wrong. I'm trying to capture and edit video in vMix from an Elgato card and from a BlackMagic Design Intensity Pro. After I capture the file, I want to edit it with VideoReDo because it doesn't re-encode an MP4 file. The problem is, as I'm told, that vMix and several other capture programs I've tried write the first GOPs as 45 seconds long. They should be only a few seconds long. There is a setting in vMix that is set to 2 that is supposed to control the capture length, but I haven't been able to get it to work that way.

For starters, does anyone have any idea what GOPs are and how they are controlled? If so, how can I control them? There is a setting that YouTube requires to be 2, but I don't remember what it's called. That setting is supposedly related to GOP size.