I wish you could get MPEG Streamclip on modern Macs. I miss it. I wouldn’t need it very often but it’s nice to have in the toolkit. QuickTime X can do demuxing but I don’t think it can do muxing. Perhaps I can virtualise Mountain Lion and install MPEG Streamclip in there.
[EDIT: I don’t want to use a video editor because I think that always means transcoding at export time. I try hard to just do minor adjustments to videos (trimming) without transcoding because transcoding means a slight deterioration of the picture each time.]