Ok you confirm what I was thinking, because even with the “loss” the video quality seems the same between both formats, and demuxing the m2ts file through avidemux gives a h264 video file of the exact same weight as the mkv video file only… don’t know if I’m clear but it kinda proves the “overhead” space wasted you’ve mentioned.
Thanks for your answer !
… just now something I don’t get: aren’t mkvmerge and mkvtoolnix the exact same tools ?