[FFmpeg-user] "-acodec copy -vcodec copy" output smaller than original

[Olexandr Melnyk]

Howdy, my intention is to split a big video file into smaller chunks for
more convenient storage and transfer.

At one point I figured that the total amount of space the chunks produced by
ffmpeg are taking is smaller than the size of the original file.

Then I noticed the above is true even if I just copy both streams from the
start to the end into one file:

ffmpeg -i Svalbard2016_g04033.mp4 -acodec copy -vcodec copy -map 0
output.mp4

Here, the output file I'm getting is 5MB smaller than the source file. And
if I do the same for a bigger source file, the size difference is bigger as
well.
Any thoughts why this is happening?

I'm going to delete the source files eventually, hence I'm afraid if I'm
losing anything (metadata?) in the process.

Source file:
https://dl.dropboxusercontent.com/u/30369146/Svalbard2016_g04033.mp4 (produced
with an original SJ5000+ camera, if that's of any help)

Thanks in advance.

-- 
Sincerely yours,
Olexandr Melnyk
http://omelnyk.net/