with VideoCharge Studio you can edit MKV/H264 without reencoding independently of key frames.
How do it?
for editing without reencoding very impotant possition of keyframes, you must use nearest keyframe to cut part of film and blimey is right.
But VideoCharge Studio can encode some frames to nearest keyframes, and left frames dont encode. It is very nice function!
To use this mode, you have to check "Editing" options on Format section.