[FFmpeg-user] Copy all streams, what actually ffmpeg does?

[Sub Phil]

Hi,

What does ffmpeg actually do in copying streams??
ffmpeg -i movie.mp4 -c copy copied.mp4

Indeed, as I noticed, ffmpeg changes some metatag data, but what else
because, my input file is 326,736Kb while the output is larger and is
382,819Kb.

Rmk: copied.mp4 is MD5 equivalent to copied2.mp4:
ffmpeg -i movie.mp4 -c copy -map_metadata -1 copied2.mp4

So what kind of modification/fixing does ffmpeg do vs a file copy???

Thanks,

Phil