When I ran into this, it came down to if I wanted to splice two videos together, or re-encode them. Due to how keyframes work, cutting on keyframe boundaries i

When I ran into this, it came down to if I wanted to splice two videos together, or re-encode them. Due to how keyframes work, cutting on keyframe boundaries is a lot faster and easier and doesn't require re-encoding in many cases. This is the default for the segment muxer. Cutting between keyframes is a fair bit more effort, and requires re-encoding, which is why I guess it's not the default.