I’ve never liked JFS personally, I find OFS to be more friendly but that could just be because I’m used to it now. Anyway, like others have said you want to reencode every video the same way, video quality and frame rate have a really big impact on the applications performance, you don’t want to be scripting using an 8K 60fps video. Use this tool to convert to iframes, 1080 height seems to be the consensus and make sure to keep the 30fps box checked.