Slightly off-topic: Recently I needed a way to add chapter information to 200 or so local MP4 video files of varying codecs (though mostly H264). It wasn't hard

Slightly off-topic: Recently I needed a way to add chapter information to 200 or so local MP4 video files of varying codecs (though mostly H264). It wasn't hard to get the job done with FFmpeg, though I was very surprised that adding such simple metadata to an MP4 container, with `-codec copy`, takes a surprisingly long time (around 5 or so minutes for an ~8GB file). I don't know why that is, as I am unfamiliar with the MP4 container format's internals, though I do assume that no re-encoding/transcoding was done (again, due to -codec copy). And it most certainly wasn't a simply copy-paste of the video data into a new file either, as that would've been way quicker. Nevertheless I just let the script do its thing overnight.